All right, folks, I promised you a thread where you could put forth theories on why the various elements in XCOM exist and/or work the way they do, as well as theories about why what we've seen so far hasn't been quite up to our standards (for varying definitions of "standards").
So, here it is. Bring out your dead! (And by "dead" I mean "random theories, crazy conjectures, and epileptic trees*". Keep in mind, though, this is meant for serious discussion of relatively-plausible theories, regardless of how much evidence you have. Off-the-wall stuff like "It's an alien training simulation for a planned invasion of Earth, and Carter is actually one of the opposing-force AIs in the simulation" is fine, but please leave stuff like "The final boss will be Mecha Stalin, and he'll be armed with a pneumatic hammer, a sickle with a monomolecular blade, and a back-mounted cannon that shoots bionically-enhanced bears!" at the door. The former is a relatively plausible plot; the latter is just plain silly.)
So, that being said, on to the theories.
Theory the First: XCOM is like Omega Company from the Phule's Company books - a "dumping ground" for otherwise-skilled FBI agents that nobody else wants to deal with for whatever reason (he's black, he's gay, he's not a "team player", she's more competent than anyone else in my unit and it's undermining their morale, etc.).
Frankly, this is the only logical explanation I can think of for why XCOM's personnel would be so diverse despite the era the game is set in.
It'd also explain why they get assigned to investigate the various weird phenomena surrounding the alien invasion: since the XCOM division gets all of the "problem children" from other divisions (and, as such, are likely regarded as a joke by the other divisions), they're the ones who have to investigate the claims of every crank who calls in claiming that a weird black guy with glowing eyes has been stalking him for the past X days/weeks/months/etc., while the rest of the FBI works on "serious matters" (kidnappings, murders, bank robberies, Communist plots, and so on).
It's just sheer luck that they wind up dealing with an actual, verifiable alien invasion. (The jury's out on whether that's good luck or bad - though if the material from Citizen Skywatch is anything to go by, my money is on "bad".)
Theory the Second: XCOM is more successful against the alien invasion than the military because the aliens aren't expecting commando-raid tactics this early in their invasion.
Consider this: In what we've seen so far, an entire US Army encampment has been wiped out to the last man. Yet XCOM is able to kick alien butt repeatedly throughout the E3 demo.
Why? Because the aliens are used to full-fledged military responses at this point in their campaign - counterattacks using whatever the inhabitants of the target world consider to be "overwhelming firepower". The invaders, however, just keep chucking troops at the defenders until they wear down the defenders through sheer weight of numbers. Once that's done, they're able to xenoform at their leisure, while any of the original inhabitants who've survived are forced to watch impotently while it happens.
XCOM, however, doesn't deal in overwhelming firepower - they deal in quick, surgical strikes to cripple a larger enemy, and the invaders just aren't used to that except as a desperation tactic once the majority of a world's defenders are wiped out and the xenoforming process has become pretty much irreversible.
Theory the Third: XCOM agents can die; the only reason they didn't in the E3 demo is because they're using protective equipment derived from alien technology - and you might not get that equipment until after the "Find. Dr Weir" mission in the real game.
Okay, yeah, I know. You're probably thinking I'm high on something for saying this. But, again, consider this: in the 2010 trailer, an XCOM agent apparently died when one of the blob aliens in that trailer forced itself down his throat.
"But the agents in the 2011 playthrough didn't die!", I hear you saying. Well, that's probably because of the weird metallic things they were wearing - I'd wager that's some kind of protective equipment derived from alien technology. If its user is critically injured, it puts them in some kind of suspended animation until either A) you're able to revive them, or B) you complete the mission.
(If I'm right about that - and I sincerely hope I am - that could also mean that the protective gear isn't a guaranteed "get out of death free" card; after all, one of the developers said that you had to be careful when using heavy weapons such as rocket launchers and whatnot, because the splash damage could inadvertently kill things that you might want to keep alive. Everyone assumes he was talking about the aliens . . . but what if he meant you could accidentally kill your own men, too, even with the protective gear?)
Theory the Fourth: The blob monsters will show up; they'll just be an early-game enemy. The vanguard of the invading force, if you will - XCOM's version of the Floaters/Gill Men/(insert weak alien race from X-Com here).
This is just random speculation on my part - the only evidence I have that this might be the case is the 2010 trailer (in which we see victims of a blob-monster attack), and the photographs from early in the 2011 trailer (the first batch of which appears to be photographs of the victims of a blob-monster attack).
However, given how easily the blobs fall to even relatively crude weapons (at least, if the 2010 trailer is to be believed - that trailer demonstrates that pistols, shotguns, and crude incendiary grenades can dispatch the blobs with ease), it makes sense that they'd be scout units of some kind - and you generally employ scouts early in a campaign.
(Oh, and for anyone who claims that the original X-Com games didn't have blob monsters . . . might I refer you to the UFOpedia entry on the Calcinite from X-Com: Terror From The Deep? Go ahead and read it; I'll wait until you're done )
Theory the Fifth: What we've seen of XCOM isn't the real XCOM: it's an incredibly realistic simulation generated by an alien supercomputer, for the purpose of assessing what kind of a threat the human race poses to the race (or races) running the experiment - a race (or group thereof) which may not look anything like what we've seen in the preview material thus far.
No, this theory isn't original with me. It's actually based on one that Brian Damage posited a while back (though if memory serves, his version specifically stated that a small group of Ethereals was running the experiment - highly unlikely, given that apparently 2K has stated that XCOM isn't set in the same universe as the original games). A crackpot theory, perhaps, but somewhat less crackpot than Aegeri's theory that the end boss of the game will be a Mecha Stalin that shoots bionically-enhanced bears out of a cannon on its back.
(Personally, I think Aegeri needs to take a break from Command & Conquer: Red Alert 3! )
Theory the Sixth: We haven't seen the real Battlescape view yet, because the E3 demo was based on an early-game mission - one where you're not expected to field more than one or two agents to assist you.
I don't know about the rest of you, but if what's been said is true - that the Battlescape is supposed to some kind of pulled-back, slowed-down/paused tactical overview of whatever area you're in at the time - then what we saw in the E3 playthrough is probably a simplified version of that interface, geared towards smaller-scale missions; if later missions have you fielding more agents (and I think this is likely, based on how Battlescape Mode has been described), then you'll probably have a more complex command interface.
*If you're wondering what an "epileptic tree" is, it's a term I picked up in my time over at TV Tropes; it came into being after a bunch of Tropers who were into the show Lost started wondering why the trees on the island in that show were always waving back and forth, even when there was apparently no breeze. Many theories abounded - it was a hallucination, the trees were actually a herd of Sudowoodo, the characters were slightly out of phase with the island and couldn't feel the breeze, and so on - but the funniest one was that the trees were having seizures.
No, seriously, I'm not joking - one of the Lost Tropers actually suggested that the trees were having epileptic fits! (Trust me, it makes sense in context.)
Since that was the most amusing theory, the term "epileptic trees" kind of caught on amongst the general Troper population, and it became a catch-all term for theories about unexplained elements in various bits of fiction, be they sane theories or off-the-wall things like . . . well . . . epileptic trees!