Ledger obviously won because of a sympathy vote. Not that it wasn't a great performance, but superhero flicks and comedies never get their due. The absence of TDK as a best picture nominee is further proof his death led to the nomination and win.
There is some truth to the sympathy vote suspicion, but its also fair to give the man his due - it was a great performance.
I think there is something too to the thought that his depression, leading to the pills and his death, were linked to his utter submersion in the role. He didn't quite die for his art, but his method acting was such that it potentially unbalanced him. Ledger had no signs of depression or mental illness that I've heard of prior to taking on the role of the Joker. The Academy seemed to recognise that his acting method consumed him and contributed to his death. Whether the Oscar was a form of odd approval of his committment to the role I'm not quite sure.
Ledger is from Perth and so all the shit media outlets here have been going on about "Perth's Oscar". I find that offensive in way which is hard to articulate.
