Throughout history, it's women, not men, who have been seen as expendable. Up till recently, if a woman died, the man would simply take a new wife and move on while a widow taking a new wife was taboo. Furhermore, the whole tradition of dowry arose as a payment from the wife's father to the husband as a sort of payment for the husband taking care of the woman. In most cultures, boys and men are valued infinitely higher than women because they pass on the bloodline and the family name.
True, you can argue that because men are sent of to war and used to defend the family, that they are of less "value," but the point is that men are valued because they can protect the family.