I think the genders of the different races are being thought into a little too much. Gorons are seen as male mostly because they are obviously meant to be put forward as a very mascline and tribal race, a female would seem out of place, for example, the Dwarves in the Lord of the Rings.
The Zora are already a rather feminine looking race and Ruto and Rutela were most probably given breasts to make them unique and look more attractive.