According to the historical rumor mill, anyone who likes 3.x edition D&D should thank White Wolf.
WotC was big, having grown fat off of Magic: The Gathering, but they were good enough businessmen to know that M:TG would pass in time, sooner rather than later. So they began a friendship with White Wolf, to the extent that at GenCon they would host parties together...they collaborated to put out the Jihad card game, etc.
WotC (according to rumor) made some tentative bids to merge with White Wolf, because White Wolf was the most successful kid on the block in the RPG community. White Wolf rejected this advance and the friendship kind of folded.
WotC still needed someone to merge and grow with, because they knew that M:TG wasn't going to last. So, they turned their eye on the ailing TSR. TSR had sunk so far that in the last year they hosted GenCon before WotC acquired them...all of the "Special Guests" at GenCon were TSR Executives, editors and writers...as well as a handful of sci-fi/fantasy authors with products to plug.
So, WotC takes over TSR, needs to reinvent a flagging product line with new ideas and they have the capitol to do it. So...awhile later, we get 3.0.
When 3.0 was successful that enabled them to recoup their investment into TSR and the development/production costs for 3.0, however afterwards that left them mostly having broken even but without a large road stake for future growth (doesn't help that a few other products failed during this time).
So, shortly thereafter, we get 3.5. Production and development costs are negligible...sites like this one had already done most of the development they needed in their thorough critique of the game.
So they trim staff a bit to cut overhead, rewrite 3.0 to 3.5, republish and this time garner the profits they need for long term growth and stability. When the coffers run dry from that success, we'll see the real rumblings of 4.0 on the horizon.
This is just my opinion...I work in the business community, but not in the gaming business. Regardless though, I firmly believe that the success of White Wolf's World of Darkness and WotCs Magic: The Gathering were the catalysts for D&D 3.x.
Cedric