There was also a blog post somewhere about why science fiction sales have fallen. The theory was that since more women read and buy books and there's so little SF out there that appeals to women, they are instead flocking to paranormal romance because that gives them what they want.

I think I read that post, or one of its siblings. ;-)

There has always been a core of little boy geeks (of all ages) who don't want girl cooties anywhere near their slide rules and spaceships, especially if the girl who's dripping those cooties can use the slide rule and fly the space ship just as well as the little geek boy. Look up Justine Larbalestier's great feminist history of SF, Battle of the Sexes in Science Fiction - there's some wonderful stuff from the early days where all the boy geeks are writing letters to the editor about keeping SF pure and manly.

If science fiction book sales are falling because a significant proportion of women readers would rather read material that has the characters having relationships that are written in interesting, smart and sexy ways - which is happening in a lot of fantasy and paranormal romance texts - then maybe the answer is to write science fiction that includes the characters having relationships that are written in interesting, smart and sexy ways.