I really like your point about how men are more likely to be reluctant to grab a casual drink (or even one-on-one lunch, I would say) with women to talk about work because they are worried it will be seen as "flirty." Based on my experience this can have a really big impact, but I don't see it discussed very often.
Being able to have easy, casual friendships and one-on-one conversations with your coworkers can be extremely important to knowing what is going on and what you should be doing to succeed. Like you said, there are opportunities that come up in these meetings that you just don't get otherwise.
I don't think this is even a conscious decision to avoid seeming flirty a lot of the time, wanting to do things outside of work with same-gender colleagues might just feel more natural. This can make it easy to miss the fact that women are being left out, and I think a lot of men don't even realize what a disadvantage this can be.
One reason for the reluctance of personal contact outside of work is the fear of a sexual harassment suit. There have been lots of stories going around how small things have been twisted into a "hostile" work environment. In a previous workplace, they got sued by a woman who claimed that one of the employees having a britiney spears poster in his cube constituted as sexual harassment.
Also, men tend to censor what they say when women are arround.
Being able to have easy, casual friendships and one-on-one conversations with your coworkers can be extremely important to knowing what is going on and what you should be doing to succeed. Like you said, there are opportunities that come up in these meetings that you just don't get otherwise.
I don't think this is even a conscious decision to avoid seeming flirty a lot of the time, wanting to do things outside of work with same-gender colleagues might just feel more natural. This can make it easy to miss the fact that women are being left out, and I think a lot of men don't even realize what a disadvantage this can be.