Well, take Mr. Mearls's statement: "OD&D and D&D 4 are such different games that they cater to very different needs." That's the same thing I'm saying: I think they're different games (substantially, as in "such different games," not just minor differences).
Do you think Mr. Mearls is claiming that 4e is not D&D? Is he laying flamebait?
No, I think you're taking Mearl's statements far beyond what he actually stated. He said that they were different games. That's pretty much a given. I don't think anyone would seriously try to claim that OD&D and 4e are the same.
That doesn't make one D&D and the other not D&D though.
The exact statement can be made about 3e as well. 3e is pretty much completely unrelated to OD&D mechanically. I would rather hope so since there's twenty or so years of game development between the two. Yet, just as was mention that one version of Street Fighter and another version will not work on the same machine, that doesn't mean that later editions are different games.
------------
I look at it like trying to define "forest". You can't define forest by the edges - it doesn't work. Trees per square foot? Nope. But, if you're standing somewhere completely surrounded by trees, then you're likely in a forest. ((Even if it's sometimes hard to see the trees
))
D&D is the same thing to me. Earlier in the thread someone claimed that my half dragon githyanki monstrocity wasn't really playing D&D because it wasn't core. But, that's a pretty difficult thing to justify. If I'm playing Oriental Adventures (1e), am I playing D&D? If I make an adventure using nothing but Fiend Folio (1e) monsters, am I playing D&D?
Most people would say yes.
So, there has to be something a bit more quintessential to D&D than mechanics. After all, it's a mark of honor for most DM's that they kit bashed the crap out of the game for years. Yet, if you asked them, I'll bet that every one of them would say they were playing D&D, despite the filing cabinet full of stuff they've crammed into their game.
If you are playing a level based fantasy game where the players (generally) cooperate to resolve some sort of scenario presented and refereed by a DM, and, after that resolution, they gain power based on the amount of things they defeated and how much treasure they gained, and then go on to more difficult scenarios, ad infinitum, you're probably playing D&D.
Just as I have no problems with someone playing Pathfinder saying they're playing D&D, or Castles and Crusades, or pretty much whatever, I got zero problem with someone playing 4e and saying they're playing D&D.
Like I said before, if you claim that D&D is only D&D up to OD&D, then at least it's consistent. However, if you try to include 3e in D&D but then exclude 4e, I'm going to call shenanigans. It's ludicrous to think that I can play with fifteen different splats, both WOTC and 3pp and be playing D&D, but, my Dragonborn Warlord suddenly isn't.
Are they different games? Oh, of course they are. Every edition is different. The idea that OD&D and AD&D are very similar games ignores significant portions of the AD&D books. And it only gets more different the further you get.