Something I hear a lot in comparing the Linux community to the OGL community is that Linux people release their programs for free, everyone works on them and they get better.
If RPG people weren't so eager to make a buck (singular), their stuff could get improved too.
We're stifling innovation all microsoft style with our $2.50 PDFs!
Except here's the thing: it's my belief that the fact that PDF sales continue to climb, at a time when RPG sales fall generally, proves this isn't the case.
If PDFs weren't worth buying, NO ONE WOULD BUY THEM.
Yes, Virigina, there really is a thing called capitalism, and it really does work.
As for why there isn't more iteration, more "improvement", the answer is simple: while RPGs might not be art, there's enough art there that not everyone can agree on what's an improvement.
Is an improvement the most grim and gritty combat system around, where a single solid hit means grisly death or disfigurment?
Is it light and breezy rules focused on role-playing?
Is it classless, point-based and diceless?
Is it classes and levels and talent trees?
If only Ron Edwards or Mike Mearls could start a site where we could learn from them they could answer these questions!