Ahhh . . . errr . . . ummm . . . .
Well it was based on my experience; not on reading the code. Playing on Emperor I noticed I have run into a lot more Mansa, Joao, Orange, Ragnar, instead of say Saladin, Sitting Bull, Louis XIV, etc. But I haven't played a lot of Emperor level games so maybe I am mistaken.
I have played a lot of aggressive AI games though and I think it does impact AI leader selection. You will get more aggressive civs like Stalin, Churchill, Tokugawa, Monty, etc. Sometimes you don't even have one good teching civ. I also noticed in some games that when I first meet some civs in default they would be cautious but with aggressive they are annoyed . . . I've tried searching the forums to find some threads that back up my claims but I didn't find anything in the last twenty minutes. I searched for comments by Blake but couldn't come up with anything he said about Aggressive AI's effect on diplomacy. I don't believe the AI's have a bias against the human but I think there is some overall negative modifier. I may be mistaken and perhaps it is a result from having more aggressive civs but I don't think so. Anyone know more about this? Kmad?