I'm pretty sure this was an unintentional feature. Hey, maybe my thread about it from a month ago in the Bug Reports section would have received more attention if it had the words "AI" and "cheat" in the title...
Regarding the AI's map knowledge, it definitely doesn't have knowledge of unexplored terrain, but there is an oversight in the yield calculator which effectively hints to it (and to the player through the recommended locations) about yet-to-be-revealed resources, which will be fixed next patch.
@Mr Blonde: You're not quite understanding the issue there. A city which is taken has its culture, and therefore defence bonus, reduced to zero (unless any fortifications survive the capture), but one which is REtaken has it miraculously restored, even if it was previously bombarded to zero. All that is needed to fix this is for the cultural defence bonus to be set to zero in ANY city which is taken, and then allowed to recover in the same way it does now if bombardment is halted.