Ridiculous statement. Just because people didn't like Nicholson as Joker doesn't mean they're protecting Heath, and it doesn't mean they're wrong.
He just wasn't dark enough, scary enough, or crazy enough for me. He wasn't a bad interpretation of the Joker, and he was true to the character in a cheesy traditional way, but I just didn't really like what he did. I hated the fact that he was fat, I hated the fact that he was old, and I hated the fact that he seemed like Jack Nicholson x2 instead of the Joker. I never bought him.
Part of my dislike for the character isn't Nicholson's fault, such as him killing Batman's parents, etc. but to me, Jack Nicholson was never the definitive Joker -- I just don't like him in the part, and a lot of Batman and Joker fans agree.
I've never seen a Joker I like more than Hamil in TAS, but I'm excited because I think Heath will pass that.