In the new Iron Man movie, Tony Stark tells Jarvis to "throw a little hot rod red" onto the new suit. Cars are a big part of his character, and what he drives matches his sleek, shiny image, both attitude-wise and color-wise. With Batman, it almost goes without saying. He's got a friggin batmobile, it matches him colorfully and stylistically.
I didn't see the new Hulk movie, but I somehow doubt Bruce Banner comes with any sweet wheels. The problem with Hulk is, he just reminds me of a
John Deere.