It's some of undeterminate without data on longevity because on the other hand we could hypothesize that even with equal gender representation initially maybe men would stay longer because women want to spend time raising children and that would skew things. Also, there might be some self filtering as you described in the last sentence where I could speculate that maybe the average man is used to being rejected a lot so they apply more to places that are hailed as hard to get into, though with the 30% figure female representation in CS touted elsewhere in this thread, it leaves the question where are these 30% women going to in CS?