It has been measured in the sciences, and a lot of that was raised recently in the aftermath of Lawrence Summers' unfortunate remarks of speculation as to why more women weren't sticking with sciences.
Macho culture can be a turn-off. It doesn't have to get down to genetics or Jungian analysis. I wish I had some links handy, but just some googling should reveal some results for anyone interested -- especially the remarks of women in science academia.
Is it the same thing in CS and related professions? I don't know, but there certainly was plenty said along these lines in the Deeply Geeky session at BlogHer last year.
I do feel that the assumption that CS and IT are meritocracies is a rather limited view, though. It reflects a rather narrow view of what these fields really are about. While there's an element of mathematics, yes, they are also inherently creative, and what you create and how you choose to create it is not something that is easily objectively measured. Have 10 people program a module to achieve x and you will get 10 different programs going about it in different ways ... even if it's all guys. Add women in there and you get even more diverse results.
So how does one measure merit in such a field?