If Domino's and other what you perceive to be 'low-quality' pizza places are truly flooding the market, then it is because a majority of people have selected that standard of pizza as their favorite. Consumers have determined that they prefer lower costs to high quality product, and thus their perception of quality is not so much based on the pizza itself, but rather on a cost-to-quality ration, with preference leaning heavily toward low cost.
In order for this example to apply to the D20 OGL market, the same consumer preference for "low cost over quality" would have to apply . . . and I'm not convinced it does. Consumers always fix the market. If they do not buy a product, similar products cease to be made. In the pizza example, a consumer may choose a cheap pizza over a thick and tasty one. However, in an OGL PDF market, I would expect consumers to choose products that actually appeal to them in terms of quality and content, and therefore lower-quality products would not be purchased, and henceforth not be made, thus virtually ridding the market of crap. It's much more conceivable to buy a pizza that can be 'good enough' than it is to continuously purchase crappy PDFs that one would never use.
~ fissionessence