Unfortunately, that argument doesn't always work - hence the phrase "leaky pipeline". I don't know specifically for US maths professors, but in many situations where women are in a small minority a situation where the proportion of women goes down as you go up the hierarchy has persisted for many years.
That is very true. I noticed that the math department of my local public university (Sonoma State University) has much higher female ratio. More than half of faculty and staff are women. This may have something to do with the more progressive culture in California as well as the fact that SSU is not a highly ranked university.
This makes perfect sense. Women's progress in math will not started at Harvard. So beating up Mr. Summer won't solve the problem. It starts from the lower ranking universities and works its way up. This may take decades to get to Harvard but the trend is clearly there.
