The primary reason we decided to do the Pathfinder RPG was because we wanted to keep producing the same types of adventures and sourcebooks we've been (quite successfully) producing for 3.5 for years now. With WotC's move to 4th edition, the 3.5 rulebooks no longer are in print. For now, sure, they're still relatively easy to find, but we wanted a core rulebook in print that isn't doomed to become harder and harder to find in stores as the years roll on—and that meant we had to print a rulebook ourselves. We can't just reprint the SRD, because two key parts of the rules (ability score generation and how to hand out experience points and level up your character) aren't in the OGL or SRD. We'd have to remake those rules anyway. And if we're remaking those rules, why stop there? Why not look at ways to improve the game to support the types of adventures and sourcebooks we're producing, while keeping close to the spirit of the rules and the game?
And then, why not open the Beta playtest to the public?
In the end, all of the Adventure Paths and modules and sourcebooks we'll be printing after this August when we officially make the move to the PFRPG will be pretty easy for folks who prefer to run 3.0 or 3.5 games to use. Stat blocks will look the same. Spells will be named the same. The classes and races are the same. The mechanics are different, yes, but that's no different than running "The Sunless Citadel" for a 3.5 game, or Shackled City for a 3.0 game (or 1st or 2nd edition game, for that matter).
In any event, we WILL be providing a conversion book to ease the transition of 3.5 to PFRPG, or PFRPG to 3.5. And the physical difference between a Pre-PFRPG Paizo product and a Post-PFRPG Paizo product should be pretty similar... I don't suspect that, at a glance, it'll be easy to tell the difference.
Anyway... please try to keep tempers moderated—the hobby's big enough for all of us!
EDIT: And yes... the OGL, which is the rules that the PFRPG is based on, cannot be revoked. It is forever, as long as folks keep using it. The only way it can be "revoked" is if it's allowed to fade away into internet obscurity, I suppose, like "All Your Base" and the hamster dance.