The title of this post is taken directly from an article in the Financial Times that describes the known gap in gender and IT -- specifically, that women use IT, and that girls feel IT is "cool" somewhere in the 90% range (the details are in the article, do not trust my memory only) -- so, why?
Shame they missed SIGCSE 2008, maybe they could have come down with us in the trenches of teaching computing and see some of the realities we all see. Another shame is that women may be adding a set of skills presently underrepresented, and needed (see Mark Guzdial's blog post about "computing + X").
I still think it is about access in the most general (perhaps most ideal) sense of the word -- looking at the research in so many other fields about the differences between men and women, we need to think differently, think about flexibility, adaptability, all the good HCI stuff -- do that for a decade or two, and perhaps things will change a bit (I will certainly be changed in that I will be looking to use those retirement funds :-).
Also, I just wanted to send out thanks to the Sisters Rodger -- Sandra for taking so many photos of SIGCSE 2008, and Susan for putting the photo albums online for all to see -- if you missed the Symposium, you can venture to the albums, but be warned, it will just remind you of what a great conference it was -- and perhaps motivate you to work on your SIGCSE 2009 research/writing earlier, get funding and make travel/lodgings plans ASAP.