My friend Tim is probably the biggest "pure" D&D fan I know. AD&D (2e) was his first RPG, and it's about all he wanted to play for years. To this day, nothing would make him happier than the prospect of playing nothing but D&D for all the rest of his gaming days.
When 4e came out he ordered the three volume slipcase. Shortly after going over the new rulebooks he pronounced Fourth Edition "the best version of D&D yet." I knew at the time what he meant. He was speaking in a strictly linear fashion--1e begat 2e begat 3e begat 4e. I know that's how he meant it because, despite his fandom, he's not really all that into "the industry" side of the hobby. There's a big part of him that, I think, still looks at D&D the way we all looked at it 10, 15 years ago, when it was this monolithic FRPG that everyone wanted to emulate but couldn't quite do directly (and thus you have the fantasy heartbreaker phenomenon).
Today I linked Tim to a post over on RPG Blog II about the layoffs at Wizards, in part because I figured he hadn't heard about the WotC layoffs yet (not being plugged in to that side of the gaming hobby, after all), but specifically because I wanted to point out that the gutting of Wizards' digital team means that, in all likelihood, D&D Interactive is indeed vaporware. Which is a shame, since Tim was basically planning on using DDI to run a campaign...once it came out.
But I digress.
All this talk over on Zachary's blog of the various options as we look towards an uncertain future for 4e got me thinking about Tim's view of D&D and its linear evolution. Certainly there was indeed a linear evolution from 1e to 2e (but even then we're conveniently ignoring the parallel evolution of "Basic" D&D). And one could argue that the 1e/2e monster led to the "simplification" that was a primary design goal behind 3e's initial release. But thanks to the SRD, we started seeing mutations. Initially, these were viewed as mere variants or mods of the D&D, the "real thing." But I'm thinking now that those mutations have become full-fledged species. And it occurs to me now, as I posted in a comment over on the RPG Blog II, that there no longer is a D&D. At least not in the way we used to understand it. It is no longer a question of authenticity, but availability.