I think it's the planning it takes to bring your work clothes, hygiene supplies that stops most women from commuting. I would be one of those fussy people, according to some, but I also love to sweat and I don't mind getting dirty. I wear make up all of the time when going out of the house, not when doing serious riding or running, of course, but if I am doing errands, you might see some. Also, I think that in big cities, especially NYC, there is such a fashion sense, it seems inconceivable to some women that they could walk into work in sweaty bike clothes and have someone see them, even if it was when they were just going to the bathroom or locker room to change into work attire. I get the sense that a lot of women don't like to sweat, based on my own anecdotal evidence from my regular friends. So, they go to an air conditioned gym, where it's "OK" to exert one's self in that environment, shower, and get back to real life.
I had a funny experience that showed me some of those attitudes last summer. I rode my Jamis to Concord center, because I was bored. It was a very, very hot day, in the low nineties. This is only a 4 mile ride, but I was sweating like crazy when I arrived. A very nice boutique that has shops in 3-4 upscale towns was having a sale, and I thought I would go in to see if they had anything. I was wearing "fashionable" commuting clothes, that I love; a skort, a Terry Eurohalter, matching socks, and my Keen sandals (which match my blue Jamis). OK, I had some women actually look at me with fright, disdain, and back away, because I was sweaty. I saw a couple saying something about me, in my disheveled state.
I really wanted to try on a sundress there, but I was too sweaty, so I just bought it and stuck it in my pannier, and it did fit. The sales staff was nice, but I was kind of amazed that my sweaty presence caused such an uproar.