Perhaps dark-skinned women have been "taught" to be "tough" because of their life experiences of being treated as "less-than" by both white and black people alike. Being black means adopting a thick skin because you expect to be insulted a great deal of the time by the circumstances of your life. Being dark and female means taking on not only the hatred of the white community, but also the self-hatred of the black community.
If I were one of the desired light-skinned, "good-haired" women who everyone treated demonstrably better than others, then I might be "gentle" too. People are not born the way they are. We become the way we are by how we're treated. When I see men with darker-skinned women, I respect them more because they haven't been fooled by the traditional standards of physical beauty and, I presume, values the woman for who she is.