And yet another perspective...
Keeping with the "discussion of the d20 system's affects on the industry" let me present the view of a new freelance writer. Note that I don't have any more authority here than a non-writer, I was just stating it so people know my perspective.
The d20 system has been, for me, all about possibilities. I now have a writing career with multiple sourcebooks written or pending because of d20. Before, there just wasn't the market for freelancers. Now, I can write and be published. It's an incredible feeling to know that someone might pick up my work and think it's worth some money, much less time and attention! Likewise, ideas that might not have gone beyond my gaming group will now reach thousands of people! I'm able to afford college this year because of my freelance writing -- if it weren't for the d20 system, I'd have had to take a year off to work in some other job in order to pay for another year of school. How cool is that? And yeah, it's a career now. It's something that I could concievably do for the rest of my life, whereas before my writing was little more than something to please people who found my website. I mean, does that not strike a chord with any entrepeneur out there?
Those that compare d20 to Microsoft (of which there has been thankfully little in this thread) would be more appropriate comparing d20 to Linux: open source, basic structure, distributed far and wide, and easily modified by developers. I think the OGL has done more FOR the industry than any other development in the last, what, 20 years? I've only been playing for around the last 15, so I'm not entirely sure. The fact is that it's moving products that would otherwise never see the light of day before it came around, and that can't be a bad thing to me.
The real question is: where do we go from here? I think if the software model teaches us anything, it's that we go up. I think as more companies use OGL instead of normal d20 (or, heaven forbid, open up straight d20 material to OGL) then we'll see a more free exchange of good, solid ideas. I mean, look at what's happening now. Soon I should be able to start up my own gaming company and publish PDF supplements for Mutants and Masterminds. Green Ronin makes more money off more core books being sold, I make money off of my work, and we're all happy campers. (Note: I'm not planning on doing that, just using it as an example). That's just amazing to me. It's nearing a free exchange of ideas on a platform that reaches a large audience....all the best parts of open-source software with all the best parts of broadly distributed software.
One final note. Recently, my normal gaming group has ended its Wheel of Time campaign and moved to what we call the Rotating Game Format. Each member of the group gets 4 gaming sessions to run convention-style one-shots using whatever game they want. This allows our group to try out all those ideas we've said "Well, wouldn't it be cool to run a XXXX game?" about. My turn is up next, and I'm running Metal Gear Solid using the Spycraft game. The guy before me ran Masters of the Universe D&D. One of the guys after me is going to run Mecha Crusade, and another is going to do Greco-Roman D&D. These ideas that are cool for quick games but not exactly what we want to invest campaign-level effort into are overflowing fountains of ideas and testbeds for new concepts. And we use d20, because we can switch games and genres with minimal effort. Rotating Game Format has allowed all of my gaming group the ability to strut their stuff without waiting until the current campaign of whatever game ends.
I'm all for d20. Solid system, solid success, solid OGL concepts.