I think it probably just has the general flow of pretty much every fitness program ever. Women, being built the way we are are generally less muscular then the men. So we work at lower weights or reps or we have a longer time period to do a given exercise. It makes sense if you think about the amount of muscle a guy generally can build, he has more muscle to use to do the push up and therefore should get tired less easily because there is more muscle sharing the work.
Anyway. Thats what I think.