I'm not sure quite why there's so much debate here. I don't think there's any question that, had the rule-set and fluff (hate that word) that is D&D 4E been released by any other company, then perhaps the majority of D&D 3.5E players would be referring to it with such names as "Fantasy Heartbreaker".
I think anyone who has read my thread on having actually run 4E knows I like the game (on balance), but for my money, it's certainly a "Fantasy Heartbreaker", only, it's one of the good ones.
I suspect that had another company released it, and say 3.5E was continuing, we'd see plenty of people switching over to it, and saying "This is EVEN MORE D&D than 3.5E!".
I guess the issue in the end is what constitutes D&D, so maybe that's why the debate keeps going (that and people love a good argument!). For me, D&D is pretty specific IP, with some pretty specific elements.
4E has most of them. It doesn't, for my money, have all of them. What really separates 4E from previous editions is that it's designers have decided to sacrifice certain things to ensure the best possible experience for an encounter-based level up game. I think this is why people start ranting about MMORPGs. Not entirely accurately, of course, because many earlier ones didn't make many sacrifices for this. But WoW does. Guided player experience is absolutely paramount. Everything has to be doable, everything has to be balanced, the right amount of treasure must be given, not too much, not too little, and the game must be fun, even if that means sacrificing the believability of the game-world to some extent. The extreme intensity of this focus, and the success with which it's achieved makes 4E seem, to me, not quite like "D&D", but some kind of hyper-refined D&D-inspired game. Heck, maybe it just doesn't have enough warts to seem like D&D, maybe that's it.