I just watched a spectacular explanation of why this won't happen. On a replay of ME2, I sent Miranda behind cover. A single, heavily wounded enemy had managed to get behind the front of the team. Miranda popped out of cover, trying to get some distance between herself and the wounded mook. She walked out in the open backwards right into three enemies with flamethrowers and a krogan. She went down faster than you can say, "Too Dumb to Live." Meanwhile, I finished the wounded enemy with a single shot, fell back, and was able to continually draw the enemies down the corridor until they'd all been worn down by Shepard's biotic attacks. All enemies dead, Miranda gets back up, Shepard's shields never went down. The game never figured out what I was doing, even though there were ample pathways they could have taken to try to corner or flank my position.
While some games try to do make the NPCs act like human players (FEAR's big claim to fame was having AI that managed to be a little less stupid than most), the biggest problem with this is our current limitations on writing code for the NPC's behavior. This isn't just a lack of computational power; writing scripts for AI is one of the toughest jobs for programmers. This is why many programmers have to use shortcuts and let the machine "cheat." Getting the NPCs to respond in distinctly human ways is damn hard to do. Also, once you write the code, human players can respond with novel ideas on the spot. The code can't; it does what you've written, and therefore winds up predictable and exploitable.
So...don't expect bots to act believably like people any time soon.
Edit: I was also told this is why in certain games, it seems the enemy knows where you are the second they are alerted by an attack from a hidden attacker, say, a sniper. (Remember the Zero Punctuation review of Battlefield: Bad Company 2?) Programming the AI to respond to an attack from an unknown direction by having it take cover, search for the shooter, then engage and try to maneuver against the sniper (the "correct" solution, ignoring the possibility of just calling down indirect on him) is a lot more difficult than simply having it turn and advance on a sniper. This is also why AIs in RTSes often cheat and ignore unit limitations or resource limitations, why fighting games can have different priority for AI opponents than humans, etc ad nauseum. It's just hard to code something than can keep up with a real person.
But wondered if it would be a nice little add on to a game to maybe have the NPC's playing on the same difficult as you, having to use tactics like you do to progress through the missions. Thoughts?