Well, the difference between race and gender is that most women have children, which take up a lot of time and require taking at least some time away from work. If the difference is due to cultural issues then maybe it makes sense to worry about the differences and try to address them, but if the difference just comes down to women have children so they work less that's a less compelling reason to try to equalize men's and women's wages (and as I noted, in some areas young women out earn men already, partly because they tend to be more educated).