Chef Aid vs Series Celebrity Voices

Okay, so in the normal episodes all the celebrities are impersonated. What about on South Park : Chef Aid? They sound very real to me.... And what about that "Behind the Menu - Jerome 'Chef' McElroy" on CC? How did they get the stars to say those things?

The Pacifist

Elton John must have a sense of humour. Who would have thought it?

Actually, he does. :) I've seen him on quite a few talk shows, and he did have a sense of humor. :)