Wicht
Hero
This is one thing I love about Pathfinder - because they are publishing under OGL, they HAVE to make their rules OGL too. No proprietary rules here. Towards the end of 3.5, this was a major problem - there was so much non-OGL stuff out there than the game as a whole could no longer be said to be OGL and couldn't be used for new OGL projects.
You are not quite right. They only have to make those rules directly fashioned off of OGL material OGL. They have published plenty of stuffy they could have been proprietary about, but aren't.