In my delirium last week, I often found myself thinking back to my own early experiences playing D&D. What I remembered again and again was that, at the time, we simply called ourselves "D&D players" without any qualifications. We didn't say, for example, that we were AD&D players, even though we all generated our characters according to the specifications in the AD&D Players Handbook. Neither did we call ourselves "B/X D&D players," even though we generally referred to those two thin volumes when we had a question about some basic mechanic of the game, like setting spears against a charge or handling NPC morale. The same could be said of Holmes, which I continued to carry around with me for years, using bits and pieces of its rules in my games without once thinking they were the "wrong" rules.
It's a funny thing when I think about it, because I know that the splitting of OD&D into two "flavors" -- D&D and AD&D -- was intended to present the game to two very different audiences, one more "casual" and one more serious. In practice, though, I found nearly everyone with whom I played D&D to be playing some Frankenstein's monster-like mish-mash of multiple rules sets. And because the rules were, with very few exceptions, completely compatible with one another, it was easy to grab a Moldvay Basic Rules, a Monster Manual, and some dice and have at it without any difficulty whatsoever. The "vastness" of the differences between the flavors of the game is often exaggerated in retrospect and was in fact more artificial than real. To us, it was all just "D&D" without distinction.
That's probably why I grab all the retro-clones I can. In my Dwimmermount campaign, the baseline is Swords & Wizardry, but I use a couple of rules from Labyrinth Lord and am considering adoptiong some from Spellcraft & Swordplay and OSRIC as well. To me, that's how I've always played D&D. I never played it completely by the book and I never met anyone who did. But then that's because these games are generally so mechanically simple that such mixing and matching is not only easy but intuitive. They share so many characteristics that I don't really consider them different games at all so much as different presentations of the same game.
Which is absolutely awesome.