So just to be perfectly clear, it's not the fact that the rules in 4th edition are different or that there's a "decency clause" in the GSL that won't let us "tell our stories the way we want to" that, honestly, was the main element that convinced us at Paizo that we were better off with 3.5/Pathfinder RPG. Rules are in large part irrelevant to story, and the fact that many are playing Pathifnder adventures with 4th edition rules is proof of that. Likewise, while we DO skew toward more mature content, we don't have to—we operated under the same "decency clause" with Dragon and Dungeon, after all, and were able to do pretty much everything we wanted to do there.
No, the real problem is the fact that the GSL prohibits you from redefining things. As I read the GSL, if you do a GSL product, you have to present goblins, succubi, eladrin, the Abyss, and everything else in the game in the way (both rules and flavor) that D&D presents it. We wouldn't have been able to redesign goblins the way we did in Pathfinder #1, nor would we have been able to make the changes to drow that we did in Second Darknss had we been using the GSL. THAT'S what we meant, really, when we said that it won't let us tell the stories the way we want.
Another part of the problem is that if we went with the GSL, we'd be handing a big chunk of our destiny back to WotC, since they can change or revoke or adjust the GSL whenever they want. That includes 4 to 10 or more years from now... the folk who control the GSL today will not remain the same folk (with the same desires and opinions) forever. It's not good business to base your entire publishing concern on a foundation that someone else controls and can change (or remove) at any time.
Furthermore, I can certainly say this: not being beholden to another master is incredibly liberating. The loss of the magazine licenses and then the loss of a supported and in-print rules set have caused an incredible amount of stress and worry here at Paizo. Both were things we had no control over, and when you have key underlying elements of a business that you have no control over, that's a recipe for doom. With the switch to Pathfinder RPG, Pazio is, for pretty much the first time, flying under its own control; we're free to succeed or fail on our own, without worry of having the rug yanked out from under us just as we're getting our footing. I'm pretty excited by that.