AI is artificial intelligence, this doesn't just mean it isn't intelligence because it doesn't come from a human being, intelligence is abstract. It means that it tries the best it can to be just like the real thing.

Unfortunately, we don't even know what the real thing is. So it's hard to imitate.

From what i understand (admitted, not very much) most modern games use a rule-base AI, essentially a series of if-then rules that can't change.

Now it is possible to go beyond this point, adaptable AI is possible in theory, but I think it is still too complex to use in games (processor demands).

Now about UT, I never played it, do the bots really work together ? Getting them to attack from different positions doesn't seem to hard (just assign a penalty if they get to close to eachother).

From my limited knowledge of 'intelligent' search algorithmes, it really does take an expert to use them correctly.