While a forum thread seems to be tracking all the details, one thing strikes me about their announcement: it doesn’t make any mention of the Open Gaming License (OGL) or the d20 System. Since WotC has the power to revoke the latter, I’m assuming that they will soon do so, probably as quietly as possible. So you may want to download the SRD while you still can. Update: Evidently, during a press conference, Wizards did state that 4th Edition would use OGL and a new SRD. This still doesn’t prevent them from revoking d20, however.
One other interesting bit is their on-line strategy, which really does look a bit like they are trying to pull a Steve Jackson and become the central, perhaps only, online hub for the game, all built around the horribly named Gleemax. Though I can’t find a more official link, in another forum post, something called “D&D Insider Fact Sheet” is reproduced, claiming this is “one community to rule them all”.
You can bet that non-WotC publishers of d20 games will be scrambling. Perhaps they will move to Green Ronin’s True20 license, which seems to have been constructed specifically to deal with this eventuality.
Wizards is clearly betting that their fan base will follow them. I’m not sure that’s true. It’s not clear to me if the Third Edition succeeded on its own merits, or because the OGL and d20 gave players a much larger and more diverse product line. I suspect the latter.