The argument over why girls don't play videogames has been raging practically ever since gaming began, but Brenda Laurel sums it up pretty well in this presentation from 1998.
Before you fire up your "I know plenty of chicks who game!" fire and brimstone, note that Laurel is specifically talking about little girls, those age 8 to 12 years old. While things have certainly changed over the course of the past decade, many points Laurel brings up still ring very, very true.
Most striking for me personally are her comments on two types of reviewers: hardcore guy gamers who think they know what games should be and "a certain flavor of feminist who thinks they know what little girls ought to be." Laurel sagely points out that neither group seems particularly interested in actually listening to the girls themselves. "It's funny to me that these interesting odd bedfellows have one thing in common. They haven't looked at children, and they're certainly not demonstrating any love for them," she says.
Even if you're not particularly interested in the question of how to get a 9-year old girl to play a computer game, Laurel's presentation is a valuable reminder that paying attention to your audience is a smart way to make a successful game.
Fair warning - the first six minutes of the presentation are a bit on the dry side, as Laurel recounts the research that brought her to help create successful PC games for girls. Feel free to skip on through it if your eyes start glazing over; the real meat is in the second half of the video.