For an interesting discussion of the findings, see Jake Young's post at the Pure Pedantry blog titled "Participation explains gender differences in the proportion Chess grandmasters," where he notes the following:
"I am going to make an analogy to make this data make more sense. Why does it seem like the US has substantially fewer good soccer players than the rest of the world? We clearly have good athletes. We play other sports well. We train athletes just as well. Why do other countries do so much better?
The answer is that when you are a good athlete in the US, you do not play soccer. You end up playing something else like football or basketball. The difference in performance is related to a difference in participation.
This data strongly argues that the difference in performance of women in chess is also a problem of participation. The problem is not that women can't play chess well. The problem is that enough women who play chess well are not choosing to play chess."