Why didn't they include more of Heath Ledger in the Dark Knight Special Edition DVD?

I was very excited when it came to DVD. I bought it the day it came out!! But the special features included behind-the-scenes footage about the Bat suit, the Bat pod, and the music, some background to events in the movie plus a variety of trailers, poster art, and more but with all the hype about Heath Ledger's performance and the character he created, etc...THERE WAS NOTHING on the joker/heath ledger........why? are they going to re-release the dvd with a 2nd Special Edition covering Heath Ledger and the joker any time soon?