From all accounts, the 3rd party 3e experiment was a pretty good success, and I think in tinkering with it, WotC is kind of messing with a good thing and being overly analytical about something that needs a light touch.
See, I really question the truth of this.
When 3e hit the bricks, you had dozens, several dozen at least, of 3rd party publishers cranking out books. By the time 3.5 rolled around, the herd had thinned considerably. By this time last year, even before the 4e announcement, you had what, 4 maybe 5 companies producing D&D supplements?
In 8 years, we went from more companies than you could comfortably count, to about one hand worth of 3rd party publishers. And, of those, companies like Green Ronin were barely doing any 3e material.
Is that really a success? When the overwhelming majority of companies drop out of the field within 5 years? When you have basically five companies competing for the 20% of the market not dominated by WOTC? ((Note, that figure is totally made up))
For the vast majority of gamers, losing the 3rd party publishers would have zero impact on their games.
I'm one that it would impact honestly. My shelves are much more 3rd party than WOTC, but, even so, I know that in the group I play in, no one would miss a step if 4e was completely closed.