Are the majority of cases due to bullying or being "forced" out of the role? I doubt it. It's more likely to be related to opportunities and different types of people gravitating to what sort of jobs suit them best. I suspect if women are crashing out of IT, it might be because it's not a particularly appealing or novel career anymore (back in the 90s it was portrayed as super high paid and "cool" - far more appealing than the very sexist financial industry at the time) and women have better opportunities to do other things than ever before (e.g. finance, management, legal) whereas males in IT are probably there because they picked it from the start as a calling rather than a career.
Update: As one of the respondents says, yes, let's make IT more inclusive. But let's not 1) assume IT is a special case, or 2) go OTT by doling out blame or restricting the largely innocent (i.e. "men" as a group) by redefining acceptable behavior to be a tiny gamut of unnatural neutrality and inoffensiveness.
1: http://news.bbc.co.uk/1/hi/education/7838273.stm 2: http://www.askamum.co.uk/News/Search-Results/Current-news/Pr...