Also, and this is just my personal opinion of course, but many might share it, the stuff that WotC produces is just head and shoulders above what they produced for 3.x. Sure, there is some debate regarding the forgotten realms campaign stuff, but the rest has been very well received. Dragon is about a 100 times more balanced and useful (the crunch anyway) than before. All in all, maybe there is just less need of 3PP's than before.
Could they improve certain areas? Yes indeed, not everything is perfect. But it's definitely far better than during the last edition, IMO, YMMV, ETC.
Cheers
Well, I don't actually own any modules, or subscribe to DDI, but based on what I *HAVE* read (KotS, FR books) and seen on the WoTC site (excerpts from several modules plus map galleries), my own opinion is that when it comes to adventures, there is *very* little quality control at WoTC these days. In fact, most of those modules are based on the premise that exciting combats (especially with "interesting" use of terrain) = fun. No regard to good backstories or logical motivations for villains, and the maps (these days, apparently, consisting mostly of utilizing the dungeon tiles -- at least if the 'Kingdom of the Ghouls' and 'Nightwyrm Fortress' serve as proof) are so unexciting and bland that as a DM I wouldn't run the adventures without redrawing them all. In fact, I'm reminded of the arrogance/hubris during the TSR era, when they were churning out stuff with the philosophy that "anything we publish, they'll buy, because we're the only official publisher doing it".
To be frank, if the map galleries and excerpts are anything to judge these products by, I wouldn't run them even if they were completely free. I would not accept them even if I could get the *printed* copies for free (space on my book shelf is limited, after all). I'd rather run the 'Marco Volo'-series in all its "awesomeness", and that is saying a lot.
So, it's only my own opinion, but I honestly think that when we're talking about published adventures, most 3PPs for 3E had better quality control than WoTC these days.