Actually.. to be serious....
It may very well be a man only ability.
This isn't necessarily meant to be sexist.
It's more a nod back to the Sage of the 6 paths, who was male.
If the Sage had been female, then the Sharingan would be a female only trait, and i think it's really that simple.
Just because women aren't the main focus of the manga (or anime) doesn't mean they're weak. It means they're supporting characters (as in they help highlight certain aspects of the plot).
As side-characters women can still be strong, but the strength has to serve a purpose for the plotline. This is why female villains make good plot tools, since you can make a female villain strong (showing that women can be strong within the Narutoverse), and not have to waste a bunch of camera time developing there story as to why they're important.
That all said, would Naruto be better if the *** of the characters was changed? Like, all the males were female? We'd get more fan service, that's for damn sure, but i don't think that would make people like the manga more, and, if anything, would probably end up being more demeaning to women then just not including them in the giant power struggle that's going on now.