Maybe I just like listening to Tarantino, and won't mind if all movie characters spoke like him. ;)
Good genre films usually do more with less (recent example: Redbelt), but I think in Death Proof, as in most other Tarantino films, the "meat" of the characters does lie in how they talk. Perhaps it's also the precise nuances and the behavior patterns along with that, but while hearing them I'm able to paint a picture in my mind regarding who they are and where they come from, etc. I really can't think of another filmmakers in the world today who has a better understanding of how people talk.