First check out this post by Noisms.
Then read me agreeing with him.
To me what Noisms is saying is that D&D is great and is still played not just because it was the first table top RPG but because we have all bought in to it as a game... as a franchise... as a scene... as a whatever you want to call it. The point is that we have taken ownership of the game and have made it our game... or games. The D&D played at my house is my D&D and the D&D played at your house is your D&D.
The edition wars have ended. And we can all enjoy playing D&D, whether you are playing my Home-School S&W game or you are playing my buddy Kurt's 4th and a half edition game (his game is still alive even though his blog is not). No matter what your game is about... elves with swords or gorillas with plasma pistols, if it has six ability scores, d20s, and gold pieces it's D&D!
This is what the OSR/DIY D&D scene is about taking the D&D game that you play at your table and making better... and better... and better.