I think of Favreau and Downey on Iron Man and how in interviews they say they have a lot of respect for the character and it's history and they want to bring that character to the big screen in the right way.
Then I read interviews with Ledger. I get a vibe of contempt for the genre and medium as a whole. I don't know about anyone else, but I want the actor playing The Joker to have, if not admiration, at least respect for the medium in which they originated.
Honestly, if I were directing a Batman movie, or any comic book movie for that matter, I would think about the creator and all of the writers through the years. Who am I, and in a sense, who is Chris Nolan to disregard The Joker to the extent where he has no meaning anymore? No movie adaptation of Batman will be definitive, but still, have some respect for all those writers and artists that came before you.
It takes a lot of hubris to make drastic changes to a character that iconic, on both Nolan's and Ledger's part. Anyone can have the balls to go new places with characters, it takes talent to do it well and to make the characters still have the same meaning and resonance.