I was playing a map on normal last night and the AI in the early stages (within 10 turns of founding) didn't protect it's city.  Maybe it's not supposed to, but twice now I've gotten a crappy starting location and wandered about for a bit until I ran into an AI that had yet to found a city, or had just founded a city and taken theirs.  In the case where the AI hadn't founded one yet, I followed him around until he founded a good one and then took it shortly after. In that game I had already founded my first city, he was just couldn't place the city because there were spiders in the way.  In another game, my starting location had only fertile land, nothing else visible nearby so I went looking for a better place.  I found Magnar the turn before he founded his empire in a good spot.  Founding the empire pushed him out a square and me and Janus moved in right after.  Magnar, not wishing to assault the two of us stationed in his city, ran off into the wilderness and died 2 turns later.  I still could create a city with my sovereign as I had yet to do so and founded it somewhere else while adventuring on a later turn.

I just feel the AI might want to leave someone there for the 3 turns or whatever it takes to build a peasant.  Maybe this isn't a problem on the higher difficulties, but on the lower ones it doesn't exactly give the AI a fair start.