I don't think TDK got snubbed in the Best Picture category. Having seen that film, and all five nom'd for Best Picture, I can say with absolute certainty (disregarding my feelings about Batman, and speaking as a film/Oscar enthusiast) that the others definitely deserve to be there.
That being said, that doesn't mean TDK isn't a good film. It's a great film. It just means that the ones that got nominated are better. But really, are you surprised? No superhero film has ever been nominated for Best Picture. Sci-fi/Fantasy/Supernatural films rarely get the Academy's attention. In the last 50 years there have only been a handful recognized, including Star Wars, the Lord of the Rings trilogy, Raiders of the Lost Ark, E.T., Ghost, The Sixth Sense, and perhaps a couple others I could be missing. And of all those films, NONE of them have actually won, with the exception of Lord of the Rings: Return of the King. And when you take into account that there are roughly five films nominated every year, that list I gave is really just a small handful.
As far as Heath Ledger goes, I'm not going to comment on the circumstances surrounding his death because it's not relevant. But in regards to the movie, it's possible that his death may have had a small part in him being nominated, but I really don't think so. I firmly believe that he would have been nominated anyway, even if he hadn't passed away because he really did give a fantastic performance. I mean, yes it takes place during a superhero film, but the man plays a deranged homicidal sociopathic maniac. How is that different than Anthony Hopkins being nominated (and winning) for playing Hannibal Lecter in Silence of the Lambs? Plus, Heath has been recognized by the Academy before, so it's not like he was a regular, run-of-the-mill, B-list actor that suddenly became popular after his death. If that were the case, then I'd be suspicious.
