The problem, there, is that a system like Rolemaster meets all those criteria. But most people would agree that Rolemaster is not D&D.
The game shouldn't be *about* the system, but I think the system matters to the way the game plays and feels, and D&D has a history and certain "traditions" and "philosophies" in its system, as well as in its fluff. It's not a black-and-white, cut and dried issue, of course. There's plenty of wiggle room.
Nailed it, with this post and the previous one you had. I was going to use the Rolemaster example also.
Fluff means a lot, also, but that can change with the gameworld, too. The default fluff has changed in 4e, and for those who want devils, demons, and the rest to be specific entities from particular planes, well, I can understand why it wouldn't feel like D&D. Doesn't mean as much to me, but I can understand why it would to others.