What follows is pure speculation, my guess as to what happened with absolutely no facts (or even juicy rumors) to back it up.
Ryan Dancey has gone on at length about the discussions and research which led to the release of the SRD, the OGL and the d20 STL. The process was well though out and thoroughly discussed with, and modified by, the lawyers prior to release.
My guess is that last year, Wizards was going over the results of further research when a disturbing trend was discovered. While the d20 logo and license was set up as a mark of compatability with D&D (and for reasons of legal protection, ONLY a mark of compatability), consumers were beginning to identify it closely with D&D. Consumers saw it not just as a mark of compatability, though, but also read expectations of content into the logo.
The lawyers said that if the consumers were seeing the logo as a mark of content in addition to a mark of compatability, then Wizards had darn well better treat it the same way. Lots of meetings and discussions and arguments followed. Many people wanted very much to keep the license content-free. In my make-believe scenario AV was probably heavily in this camp, knowing that well done mature products (and the BoVD was just the merest first baby-step) could extend the game in a good way. But, as always, the lawyers won.
Finally, after much further gnashing of teeth and many meetings, drafts, proposals, discussions, more meetings, approvals, rewrites and delays, the new version of the d20 STL and d20 Guide were born, quietly thrust into use without warning in the dark of night...
Oh, well. As I said, just some marginally on-topic wild guesses about what might have happened in one of the infinite universes. Feel free to return your discussions of what is and isn't porn...
-Dave