Here's another theory that I will probably be flamed for -- maybe girls don't get into programming as often for the same reason that female deer don't bash heads against each other as often as the males do. Maybe it boils down to testosterone. Males of many species have an impulsive drive to accomplish certain things, and in humans' case this is largely independent of intellectual aptitude. Yes, girls are smart. Many could be good programmers. But do they want to? Are they driven to? Am I (at least partially) driven to my peculiar lifestyle of being glued to a screen and eschewing much social interaction because of testosterone? ("Yeah, you'd like to _think_ so" I can hear my naysayer naysaying.) But these are questions I honestly ask.
Yes, you should get flamed for it. Your theory does not hold water when we compare the proportion of women going into engineering in general, and software in particular, in India and China. Those proportions are greater than ours, so this is obviously a cultural issue, and not an innate female avoid-locking-horns issue.
I also find it laughable to compare software programmer's competitiveness with male horn-locking. Out of all the activities to compare, software development is the Peewee Herman of activities. If you want to discuss activities that evoke horn-locking and competitiveness then look into being a professional athlete or a member of the military.
But software development/IT? YOU. GOT. TO. BE. KIDDING.
There is a lot of misogyny in software development, specially in the US, and in particular in Silicon Valley circuits that cater to the young and brass unwashed man-boy masses. But misogyny =/= male competitiveness.
Nor does software engineering has a strange-hold on competitive behavior. There is competitiveness in law, business, sports and politics where women participate in great numbers. So the competitive drive as a factor is also a bad, flawed theory.
For all the cultural advances that our society has made, the reality is that our society pigeonholes men and women into these roles from infancy which leads to the participation % of genders in specific industries, %s that you do not see in other cultures.
Furthermore, sexism is rampant in software development, and STEM in general. So of course women do not come on board. And that so many juvenile beta-male responses are made on this forum to deny the existence of sexism, or to decry some fabled "female agenda", that simply proves that sexism is indeed rampant and entrenched.