I've been playing D&D since 1979 and running an undersea campaign online since 1998. As witnessed by the release of Stormwrack, it's taken years for WotC to catch up with me.

Granted, I skipped most of 2e, so I haven't felt guilty about purchasing my fair share of 3e materials (minus supplements specifically for Eberron and FR, as I run a GH game).
Anyone familiar with the World of Greyhawk knows how divided the fan base has become. There are 1e purists, pre-Wars holdouts, 2e fans, Living Greyhawk enthusiasts, and 3e aficionados, to name a few. The same can be observed, with 3e D&D in general. There are core rules elitists, anti-WotC rebels, Min/maxers, wargamers using miniatures, and more. Some people won't play a game of D&D unless the game uses information from the core rules only; forget rule zero. Some, feeling most comfortable with "official" D&D, will only play games if the allowed material excludes third party publishers. Some feel the material in the Dragon and Dungeon magazines is unquestionably "canon". Some will acknowledge d20 and homebrew the rest.
Even in the abovementioned categories, there is fractionation, as witnessed by the "half-breeds are icky" thread. Some want only half-elves and half-orcs, some want no half-breeds at all, and then there are those who allow just about anything.
And never mind about the style of play. Some enjoy a healthy dose of "rules-lawyering", others want a rules-light in-character escapade, and others wish their D&D were more like Doom or World of Warcraft.
You can't fault WotC. They release a torrent of supplements in the hopes that some, if not all, of the players above will buy them. Yes, I have my own rules, PrCs, monsters, magic items, spells, treasures, and templates for my undersea campaign. That didn't stop me from purchasing Stormwrack the second it landed in North Carolina.