Colleen and Deb,
You are both right, I too have seen an incredible amount of "teaching" on the mat, typically by men. And yes, it does have an effect on women to a large extent (certainly not all women). I cannot tell you how many times I have trained at a seminar (in dojos where women wear hakama from the first time they step on the mat), where a man has automatically stuck out his hand to go first, and proceeded to tell me how to do something before I have even grabbed him. While it doesn't happen so much anymore (I think I've become a bit beligerent and cussed, and they can see it in my eyes), it still on occassion happens.
Womens classes wouldn't take care of that particular problem though, because I am sure some women would just take that role themselves. It is probably by in large, human nature.