What's interesting here, I think, is the way in which we're recapitulating the evolution of Original D&D - various discussions of various supplements, like here, and finding ways to adapt or recreate these systems for availability and use today. This doesn't surprise me, but there is an interesting possibility in all of this: at some point, Original D&D will have been fully re-imagined, but it's not at all clear that AD&D 1st Edition is the "natural" next step. Nothing against the fine folk who have put together OSRIC, but fairly soon we will be able to take our "Original D&D" in directions that were not thought of "back in the day" - and that will be a good thing, I think. YMMV.Victor hits several nails solidly on their heads here. Much as I love AD&D, there's very little question that its appearance between 1977 and 1979 was not a wholly organic development, except from a business standpoint. By that I mean that, if one reads editorials in The Dragon from the early days of the hobby, not to mention other fanzines and even the OD&D supplements themselves, AD&D doesn't seem to have been inevitable and one could argue quite cogently that it was in fact a volte-face on the part of TSR, a repudiation of Volume III's question, "... but why have us do any more of your imagining for you?"
I exaggerate, of course. For all its ponderousness, at its core AD&D is still a very "light" system compared to many of its contemporaries and successors. I wouldn't hesitate to call its mechanical design principles old school, though I would feel compelled to note that the way the game was sold and promoted laid the groundwork for much mischief later, both by Gary Gygax and others. AD&D was only possible in the wake of the twin legal battles with Dave Arneson and Dave Hargrave and the rise of convention play as an important element of TSR's business plan.
Let me reiterate that I'm not trying to saying AD&D is the Devil's own game or that Gary or TSR or anyone associated with those days were involved in some kind of conspiracy to suck the soul out of the hobby, as I think no such thing. However, I think it's quite possible to imagine an alternate history, one in which the inclusiveness and open-mindedness of the early days of the hobby hadn't disappeared once roleplaying became a big business. In such an environment, I don't think AD&D would have come about at all, as there'd have been no need, let alone demand, for it.
To imagine what such an alternate history might look like, you need only consider the current state of the old school renaissance. What you're seeing now is a "retro-clone" of this possible past. We have multiple games -- Swords & Wizardry, OSRIC, Labyrinth Lord, to name just three -- that all derive from the same root stock. Each is supported by a variety of third parties, as well as a fan community that freely and easily moves between them all without any sense that it's "wrong" to do so. There are fanzines and the latter-day equivalent of APAs, the blogs. This community is a chaotic, roiling mess, bubbling with creativity and discussion -- and arguments -- about how best to do this or that or what would happen if you mix these two things to build a third thing. There is no one true way here, even if there are some who will occasionally try to convince you otherwise. At the very least, there is no single True Game®, as no one has the resources to create the perception of one in the fans, who are frankly too happy with the embarrassment of riches to care anyway.
Again, I exaggerate, of course -- but only slightly. One of the reasons why I don't shirk from talk about an old school "renaissance" is because, in a very real way, this is a rebirth of the hobby. It's like it's 1977 all over again, except this time Supplement IV really is the last OD&D supplement and there will be no cease and desist orders sent to the House of the Dragon Tower.
How cool is that?