I'm going to stereotype a little here, but I think there are a few discrepancies here.
Even though I'm very... "Artistically challenged", I do consider myself a web designer. I specialize in the programming aspects of the site.
Personally, I would think females would be more inclined to do the actual layout/color scheme of a site, rather than the backboned Server Side php, or any JavaScript the site might include.
I think a more interesting question would be:
Is the percentage of women that design site layouts higher than the percentage that write actual code. And by code I mean code, not HTML. HTML is not a programming language.
Bruce