It is not only true of women, but it's specially true for them.

If a work mate is a member of the Jewish/Mormon/atheist minority, I may not even know. And if I know, it's easier to forget. If I am a man (and I am), I am not gonna forget that the person next to me is a woman.

It may be also true of, for instance, rate. There was no black people, and very few Asian and Latin American, where I studied and in most companies I've worked for.

I, of course, don't consider myself a bigot (who does), but I guess I'm as likely to hold that kind of bias against black people than woman. Or significantly more, since I have worked with several women, and I have never worked with a black person (obviously not American).