I don't know why we should focus on startups when this is a much more global issue. If you look at your typical college's CS, Engineering, or Math departments you'll find similar ratios of females as you find in the tech workforce. I have no idea why that is but it's not caused by who startups are hiring. If you look at a typical college's marketing department you'll see a lot more women, how is it surprising that there are more women in marketing positions?