I think just the fact that most of these discussions really revolve around technology is the reason that we aren't seeing many females- there just aren't that many in our field comparatively.

On the other hand, I think that another contributor is that I sort of assume everyone is male unless there is some indicator otherwise, and I'm sure most women prefer not to put themselves out there with a "Hey everyone, female here!" I wonder if there was an actual poll how many people on HN are actually female?