It is just advertised that way, the product is the same. It, however, probably contains less product in the package to accommodate men's usually shorter hair.
Because guys don't want to admit they use Clairol (or some other "feminine" brand).
It says that just for the "stud factor".
Girls should use it! Let's beat the system lol
Because men dont want to use something with a women on the box
might be some kind of ph difference in the chemicals?