I suspect women aren't attracted to computer science careers as often as men because they generally like more artistic and creative ventures. In other words, most women prefer careers and interests that allow them to be hand-on empathetic with the objects and people around them. In general, computer science is hardly portrayed as such a career. It may involve aspects of these things, but women generally aren't aware…
"…dominant culture that discourages women from even entering a computer lab filled with sweaty nerds, much less think about joining them." You have a good point here, but it's not just that they're sweaty, it's that all too often they're actively hostile to women – whether it's sexist jokes, an obsession with rape in DND games (all too frequent) or just the way they seem shocked that a woman could actually be good at…
Yes, we're all a socially inept bunch of geeks, whatever. Socially inept girls should fit right in, and the rest of the girls can do what I did - ignore it, and just focus on learning.