It's not about how many titles are released
But how many are bought and played. I think that tons of non D20 products are being released. That's to be expected. The Internet makes advertising easier, printing technology is getting better and pdfs allow people to release books without sinking lots of cash into a big print run.
But that doesn't mean that the OGL isn't doing it's job. Some people (like me) are system junkies. They love learning new ways to calculate probabilities and get all excited about bell curves, dice pools, etc. No gaming system will satisfy their desire for new stuff.
And system junkies collect games. So I'll pick up the latest edition of Paranioa, WFRP, Harp, Shadowrun, Noblis, Angel, AFMBE, etc. BUT THIS DOESN'T mean I'm playing them. What my group is playing right now is D20, specifically Iron Heroes. Collectively, our group has purchased 4 copies of the IH rulebook in the last week or so. And I'm the only one with the HARP book (which I will say is nifty). For the next 6 months to a year, we'll be playing IH weekly. I'll be adapting DnD modules (mostly from Dungeon).
4 of our players aren't system junkies and pretty much only buy the core rules of whatever game we're playing (DnD, Conan, Star Wars D20). 1 player likes D20 stuff and WOD stuff, so that's what he buys. 1 player doesn't really like D20 (but is a total GURPS-head), but games with us anyways.
This is all anecdotal since I don't have sales numbers. But I suspect Buring Wheel sells a lot less than say Earthdawn did. And while I hope HARP sells well, I bet it's less than RM 2.