What are some of the characteristics one looks for in a bike? Functionality and ease of use would be two of my priorities. So I have to admit that I cannot for the life of me understand why the typical bicycle model for men has this awkward bar situated horizontally high up on the frame. It really makes mounting and descending much more difficult. And it can cause some serious harm and injuries in sensitive places. Why are they constructed that way? I find it hard to see the logic. Unless they were invented as some early form for birth control method?
A typical bike for ladies
A typical bike for guys
Gender Observations 
Haha. The odd bar that you are referring to ensures the stiffness of the frame. We are getting closer to the technology required for the bar to become obsolete, but I guess you will have to live with the bugger unless you want the stiffness of your bike to be compromised. Although I wouldn’t count on the idea of a softer frame keeping you up at night…
So why are bikes for women built to be less stiff than those of men? The fact is that they aren’t anymore. Top female racers, such as Marianne Vos or Emma Pooley both have frames mor similar to the latter than to the former of your pictures. Your idea of a bike for women is tied up with a particular kind of bike, namely that intended for leisure rides. Those bikes are built for comfort, and the female version is still tailored after the first ones for girls, allowing you to ride it with a skirt or dress;)