My two cents:
1. My wife believes that women have too many responsibilites to do between work, kids, and the home to have time to work on tanks and so on. I tend to agree; it is much more easy for a guy to make time for a hobby, regardless of other responsibilities. Traditionally, it has always been "kids leave Daddy alone, he needs some quiet time" and then Mom ends up with the children to entertain them while Dad works on the car, repairs, hobbies, or going out with the Guys.
Kind of another example of a Glass Ceiling. I would like to point out that I do plenty around the house, have no children, and have the good fortune to spend a fair share of time at the house doing work when I am not traveling. In other words, it is easier for me to make time to spend with the tank than other people.
I also think that the relative dirtiness may have something to do with it as well. From an early age, we have all been pre-conditioned that boys go outside to play in the mud and girls stay inside to play house with their dolls. Boys get to fingerpaint when girls have crayons because they won't get their dresses messy. Guys play football, girls go to dance class.
I am, by no means, saying that this is the case for everyone "out there," nor do I believe that it is right. I think as we advance as a society, you will see more women get involved in this hobby where the numbers will either balance out or favor women.
2. One of the reasons I think women will end up populating this hobby is because I think that, as a generalization, they are more apt to see the details and design something that is more pleasing to the eye than men. Again, there are always exceptions to this. I think men can make a great overall picture prone to mistakes in the fine details. We need practice and make the time to do so until we have obtained a result that is true to the original "vision" we had. I think women would have a much easier time at this hobby then men. Alas, if only they had the time to make the time for the hobby!

(joke)
3. Oddly, I don't see many differences in styles between men and women. I think that because women tend to be more detail-oriented, they can achieve the desired effect in less time then a man. I notice that Jess and TexGal shared similarities in "collectoritis" and the tanks shared some of the same look, but were also very unique in their own right. Sunstar seems to plan well in advance and obtains a great end result as well, but I don't think that a man couldn't achieve the same result. I think that Sunstar probably achieved it faster than a man could, all things being equal. And then you have Diane Walsted who detailed out NPT; but I have seen many NPT's done by men that are pefectly similar in style as well. There have been plenty of Dutch style aquariums that have been done by both men and women, and there really is no difference from what I remember in style.
4. Drinda, Jess, Diane Walsted, Sunstar are women that I feel have stood out. Again, I don't look for who's a woman or a man while I am on here unless I am PM'ing and need to know how to address the person.