Funny thing is, originally they were going to have the mayor on Family Guy named Adam West and that was it. It wasn't actually going to be him. He just happened to show up for the audition.
LOL, I didn't know that. South Park on occasion have been offered by the actual people to voice themselves and they have specifically said no to it I guess that's a different type of deal though. It makes it funnier and aides it's crude looking production somehow if 90% of the voices are blatantly trey parker.