I don't know whether WotC uses inhouse counsel for drafting the OGL, or pays external lawyers - but either way, I think that releasing the GSL would be pretty expensive public relations. So I don't really think this is a plausible explanation.
The GSL is what it is - an experiment - as I described in my previous post.
I agree, I don't think it was PR.
Remember, one of the "selling points" internally at WOTC for the OGL back in the development of 3rd edition was "hey, these guys will write adventures, those are least profitable products!"
Of course, 3PPs could figure that out just as easily as WOTC, and so, while there were adventures made, there was also a lot of those OTHER books, the much more profitable player-focused "splats".
So I feel, with the GSL, WOTC tried to *really* have their cake and eat it too, and write a license that de facto limited 3PPs to those least profitable of products, adventures.
Except they seem not to have anticipated that there was a THIRD option other than "make anything we want" and "make adventures to support 4e":
Make Nothing for 4e.
Given that the OGL was still there, companies like Green Ronin and Paizo and RPGObjects could just keep on keeping on supporting the games they always had.
While the OGL certainly had some unintended consequences WOTC didn't like, it was on the whole a HUGE benefit to them for exactly the reasons Dancey initially proposed.
The player network moved to d20 in DROVES. It became the common tongue of RPGs. If you had a niche "long tail" rpg idea, you were much more likely to use d20, since you understood it, and the majority of players understood it.
If your idea was crazy to begin with, you can make it more appealing by at least letting people know the underlying system is solid, and that they won;t have to break their brains too much learning it.
This meant everyone was dealing with WOTC's rules all the time, and much more likely to find something of merit there to make them check out the "official stuff".
WOTC gave all that up for the chance at a few more adventures, and it failed spectacularly.
I'd also argue that a lot of the mechanical changes in 4e, which were very unpopular, were specifically designed to prevent a 3PP from "OSRIC-ing" 4e and reverse engineering it under the OGL.