The New Humanist Magazine, in its latest issue, has published an excellent article that talks about the rise in popularity of the science fiction genre in television:

No one who likes television could in all conscience have missed Heroes, Buffy the Vampire Slayer, Firefly, Angel, Battlestar Galactica, Lost or even, if you’re feeling patriotic, Dr. Who. Supernatural and extraterrestrial television has stopped being only for people who like to dress up with pointy ears, ideally at a convention with like-eared friends, and become the mainstream.

Natalie Haynes argues that sci-fi is becoming increasingly popular these days because programmes set in the real world are becoming increasingly limited in scope and because the nerds (like Joss Whedon) are becoming more powerful. She also talks about why science fiction fans are so loyal.

Anyway, it's a great article and I highly recommend you read it.