Perhaps, but it is true that the rulebooks, prior to 3e, all discouraged mass sales of magic items, and the 3e rulebooks encourage that anything within a certain budget (based on settlement size) ought to be available.
Dating back to perhaps my third campaign- waaaay back in 1982- I've seen Ye Olde Magick Shoppe run one way almost exclusively: the existence of something on the list of magic items doesn't mean it's in stock in that store at this time...or at the price you want to pay.
I run mine that way as well.
While that may be true, the OGL and d20 system basically permitted a flourishing of 3pp that provided alternative rules to those of D&D 3e, which formed the central backbone or starting point of those changes. These 3pp probably served as an excellent tool for market research, as WotC would likely be able to judge through the ENnies which products with what changes were garnering the most attention and acclaim.
Again, that is essentially a change in the market; the gaming industry- not a change in the game itself.