Did most of the people who have seen The Dark Knight, did they see it because they are fans of Batman, or?

did they go see it because of Heath Ledger's death and it is his last movie? I know these are both reasons, but which one is the biggest reason why everyone is crazy about The Dark Knight and why it has become the 2nd highest grossing movie of all time. What was a bigger reason for the anticipation of The Dark Knight: 1). the Batman franchise or 2). Heath Ledger's death and his final movie