Could it be that professional developers don't want to come home and program? Most people, male or female, want a change of pace after working all day. Not everyone can live and breathe software without a break. So, insulting professional developers is just kind of distracting because you actually made a good point and it reminded me of something I didn't say when I posted anonymously earlier.
Open Source projects are usually started by someone with a passionate interest in a problem, or maybe just an itch to scratch. Others joining the projects again have some kind of personal interest in it - either to get requested features implemented, share patches, or even evangelize if the software made that much of a difference to them. (The few times I might have been tempted to try my hand at OSS, the software was written in a different language and not one I wanted to learn. Doesn't mean I don't love my OSS, though.)
So, you're right in that these are 2 different questions. Women in IT/STEM in general isn't a useful place to start when discussing OSS participation. Maybe women don't participate in OSS as much because they don't use it as much as men do, who knows?
What might be better to study is how to motivate people to actually finish or maintain code that they throw out in Sourceforge or Google Code.
