Do you think it may also have something to do with markets and publishers? I mean, I can name several recent fantasy novels that are runaway bestsellers. I can't think of a piece of SF that's had the same luck in the past couple of years. It may be a self-fulfilling prophecy - because of the perception that SF isn't selling as well right now, less gets written because it may not sell, and less gets published...

Who knows. I read 'em both, and I seem to see about the same amount of good writing in both categories.