One of the best competitive Counter Strike Source players I've ever met told me once that I was probably the best female CS:S player he's ever met. That meant a lot to me, because this is a guy that I could never beat. It made me happy and a little proud knowing that while he was near impossible for me to beat, that he considered me to be a dangerous encounter.
I've met great girl gamers. Girls are not bad gamers. If you get a girl interested in a game, we're every bit as capable of being as super skilled as any guy. Games are often made with guys in mind. Made for guys, by guys, staring guys, killing guys, etc etc. It's a common knowledge. When a girl becomes interested, she's dangerous. I know lots of girls interested in Pokemon, and they're badass. I know a handful of girls that (like me) at one time played a first person shooter a lot, and like me, were skilled. It's a game that has all skill ranges. Like any guy, they're skilled or unskilled as the next person.
So I say it's entirely dependant on interest levels of the individual. There are common interests in specific genders, but there are still those that enjoy what's popular to either one gender.