While I think there are many times that Oscar winners who have passed on get a sympathy vote and win the statue, I don't see Ledger's performance that way.
Like I said, I was never (ever) a Batman fan, nor can I say I was ever a Ledger fan (not that I disliked him mind you). As a matter of fact beside Batman, the only movie I saw with him was his first with Mel Gibson (can't think of the name of it).
It was the quick shots of him in the previews of the film that drew me to actually go to the theater and pay money to see a Batman movie.

He made the film IMHO. I only can say I was not disappointed. I looked forward to every scene he was in.
Of course I am not the movie buff that many of you are nor do I see movies at the theater on a regular basis, BUT as far as I'm concerened Ledger earned AT LEAST a nomination for what I think was an outstanding performance, dead or alive.
TIS