Well, we have to remember that the AI's need to be tracked like players. Like, not just path finding and such (which is not memory at ALL and pretty much 100% your processor) but seeing how a player-computer would react could use a bit of memory.
It has to know quickly what not only all of its resources are, what it can and cannot see, and what new things it can do, but also it should have a list of recent actions (which is where the memory is). For example, lets say it saw a HUGE army sneaking around the outskirts of its town. Ok, in classic AI it would say "HEY! get those guys away from me" but the moment they pass out of his line of sight, he forgets about them. (or he doesn't because the AI is broken and doesn't follow the rules of fog-o-war).
Now, thats no fair. That makes him automatically much dumber than a human, because a human wouldn't forget there are guys over there... no, he'd probebly send a scout out to watch the guys (since he can't see them anymore, its suspicious) or talk to the other player to see if he can find out what he's planning and what the excuse for having an army over there is (since if you say to another human, 'whats that army doin' off port bow?' and they respond "I'm goin' to kick yellow's ass" you knowing that yellow is off that way. That's perfectly reasonable). Classic AI can't do that kind of stuff. It would require I don't even know what, and there would have to be memory alloted to holding information like that for quick reference.
Now, this is where 64-bit AI might be usefull. Again, I've only done simple AI so I don't know exactly what it would take, but I imagine that holding information like 'this guy has done this, this, this, and this which is all suspicious. But he does this and this, which means he's a nice guy and not picking a fight with me right now. I can see one of his cities, which contains this and this, which would let me assume he's not gathering an army on my boarder right now, and I know he's at war with red but the war is not amounting to something since I do not see many units heading his way so he be willing to risk a two-front if he doesn't actually start suffering some heat from red. I could try to bribe red though, give him some gold to make sure there is some heat there, I know red likes me and there is an army that could be hitting this other guy. At what price? and how can I lower it other than giving him other stuff' might be memory-hogging. thats some seriously awesome AI goin' ons right there! I don't really know what it takes to make that.