One possible reason for this is that in those countries science/engineering is often one of the few routes an educated women has available. I've only heard this anecdotally and haven't been able to research it, but it could be one factor.
I am Pavel's mom who was born and raised in USSR. I don't think that being an engineer was the only route for a woman to become educated - women could become doctors or teachers as well. As a matter of fact there were more female doctors and teachers than male. Accountant degree was also very popular and obtainable among women. I think that credo may be right - it is societal and cultural pressure that prevent girls from going into these fields.
Women in developing countries face the same problem as the women in the US on top of facing the problems that are unique to these countries.
edit: can we get a reddit-style "context" option? I want to link her to this comment, and display the two parent comments; if I just link to the 'grandparent', who knows where Scriptor's reply will end up.
If I want to show someone this comment (http://news.ycombinator.com/item?id=2783390) and the two parent replies, there's no way to do that. I can link to the grandparent, but what if the parent comment is downvoted in the meanwhile? It would show up at the very bottom.