Again, thats your frame of reference. When I was growing up, Cesar Romero was the only one who had ever played him in live action. Then along came Nicholson.
By the time Hammill came along in the cartoon, I was already in my late teens, so he just seemed like another version of it. I guess if BTAS was your first exposure to the characters I could see how you could think that. Same thing for Ledger. He's just another guy who's played the role at this point although his take was much different than any of the others.
