There are so many more guy players than girl players that you can't even compare it. As it stands, guys are better. That doesn't mean guys are inherently better, it just means they win by numbers alone.

Also, I think there's more motivation for guys than girls. Guys can play any genre of music and no one thinks anything of it. Guitar-wielding girls seem to be pretty much kept out of rock, for some reason.

And it's common knowledge that chicks dig guys who can play guitar.