Sorry I missed this earlier, but would like to comment even if I am late to the party.
Like the OP, I felt my class of fellow IDers at Pratt was a very even mix of male to female (back in 2006). Once I began working in the field however, I’ve only ever worked with one other female ID co-worker. I know that 6 years in the field is short but thanks to an “interesting” economic climate, I have worked in a variety of offices and industries.
The possible theories the OP suggests sounds more like possible determents to females choosing the ID profession, I would like to think that once they have completed their ID education most of these theories don’t make sense as an obstacle to joining the workforce.
I cannot say I have met much adversity in the workforce being a female industrial designer, most co-workers have been nothing but happy and helpful to work with me. I really enjoyed the time I have working with another female IDer, we became good friends and keep in touch even though we are on opposite sides of the Earth now (can’t say that for most of my male colleagues). I worked in lighting, medical, and footwear and felt I was treated fairly and no differently then my male colleagues.
I now work in the motorsports industry and it is very challenging, particularly as a female. I am again the one and only female designer, and not even as an Industrial designer but now as a graphic designer. I do suspect my gender played a role in which design position I was appointed to. I am not discouraged though, I have my foot in the door and will work to put myself back in the product development side of things. Perhaps this is the case with many other fellow female IDers- in order to find ourselves in the industry we want we have to take these stepping stones to leap to our desired positions.