I think genre is one of those concepts that's handy in passing conversation but slippery when you try to look at it too closely. At the surface level of "does this have swordfights and magic spells?", Mr. Raggi is entirely on the ball in calling D&D swords & sorcery. Meanwhile Mr. Paladin in Citadel points out how easily the basic assumptions of the S&S genre can be undermined in play. In actual day-to-day life I have no problem describing D&D to a newbie as something like "You play Conan, I play Gandalf. We team up to fight Dracula." On the other hand, ascribing any genre to such a wide-sweeping vehicle as D&D makes about as much sense as declaring that a clarinet is a jazz instrument. Sure, you can get a crapload of Dixieland out of the thing, but it can also play a zillion other kinds of music. I mean, have you seen the entirely awesome new pdf Terminal Space? It's friggin' OD&D in outer space, man. And you roll a new 3d6 stat for your PC called Tech Level. If you roll low enough you get to play a cave man in outer space! Put that in your genre and smoke it!
So yeah, D&D is a swords & sorcery game. That's a handy thing to say. But at some fundamental level it makes no sense, just like pretty much every other oversimplification we use in our daily lives.
19 minutes ago