@drewisfat: You're exactly right, and your point carries on to modern warfare. The Nazis invaded the USSR on 3 fronts, you could say with 3 stacks, and that was an army with millions of soldiers, thousands of tanks, etc. It's not as if they all spread out and marched across the entire border in a "carpet" of doom.
I didn't have a problem with the stacks either. Someone at Firaxis did, though, and it was almost pathological. In Civ 2 the combat was a joke, and you couldn't really stack. In Civ 3 they allowed stacks of doom to exist, and Civ 3 combat was alright, nothing special, but alright. So then in Civ 4, someone designing the game literally had a stroke every time he thought about combat involving stacks of doom, so they invented the concept of collateral damage, which was supposed to bring the end to the stack of doom... but it didn't.
Now, I want you to think about that for a minute: They released Civ 4 with a combat system revolving around powerful siege weaponry doing collateral damage, thinking that it would stop players from using a stack of doom... of course anyone who's played Civ4 knows that the best way to fight is with large stacks. So it makes me wonder, do the game designers actually play the game...like, you know, at least 2 times?? If they had bothered to play the game they would have forseen this.
So then they decided to go with 1 UPT because... you know, stacks of doom give you a stroke, or some crap. I don't understand it. I just started playing Civ 5 now and I'm going to try to appreciate it. I hope to Jeebus that the AI isn't completely useless and knows how to fight reasonably well (I doubt it), but I'm going to try to enjoy the game nonetheless. But seriously... why is it that they just can't stand stacking? Like imagine trying to play Risk without being able to put more than 1 army down per region...