Okay, I just finished reading this thread (phew!), and there's... a lot here to digest. But there's a bit in one post a ways back that nobody seems to have responded to, and while it's not terribly important to the matter at hand, I did want to respond in case anyone found it interesting:
The THEORY was that WotC was also relying, but I know of no instance where they have ever distributed anything they didn't author themselves under OGL terms. They benefited from the good will and much enlarged D&D community that the license created, maybe, but in effect they seem to, at least now think, the license is simply a form of control they can exercise over the community.
WotC
did, in fact, distribute things they didn't author themselves under OGL terms! Not much, but a few things.
In the back of the third-edition
Monster Manual II were two monsters "adopted" from Necromancer Games'
The Creature Collection. One page of the MM2 was taken up by the OGL, specifically and only because of those two monsters. The book was explicit about that:
We've printed these two descriptions at the end of the book, in a special layout, to make it clear that only these two monsters are considered Open Game Content. The rest of the material in this book is still closed content, and can't be used in other products.
Later in the same sidebar that included those sentences, the following text appeared:
Over the long term we hope to use more and more material created by the independent pool of d20 System designers and publishers, just as they are using the Open Content material created by Wizards of the Coast. Instead of reinventing the wheel, we're all able to partake of the shared design resources that operate under the Open Gaming License.
And they did it again the next year in
Unearthed Arcana!
Unearthed Arcana was released under the Open Game License—though of course it did reserve some items as product identity (the usual: proper names, artwork, trade dress, certain monsters)—, and the Copyright Notice in its Open Game License referenced
Swords of Our Fathers by The Game Mechanics and
Mutants & Masterminds by Green Ronin Publishing.
As far as I recall, though, that was the last time WotC included any third-party OGL material in its books—it's possible there are a few more instances I'm forgetting, but it certainly wasn't something they kept doing for long. I don't see any reason to doubt that they meant at the time what they wrote in the
Monster Manual II, though, about hoping to use more and more OGL material. The
MM2 and
Unearthed Arcana were both very early in the 3E product cycle, only a few years after the introduction of the OGL, and my guess—and this is of course only speculation—is that the WotC staff really
did at first fully intend to make more use of the OGL, and have more of a give-and-take with third-party publishers, but that even back then Hasbro decided it didn't like the idea and put a stop to it.