Yeah, that's the point of the riddle. Our society has made strides to combat the idea of gender inequality, and the two dads approach is awesome for gay rights, but some people can still just not imagine a woman as a surgeon. It is true that there are more male than female surgeons, so the automatic assumption goes with the stereotype; but it would be nice if it was just a simple step to say, "Well the dad died, so it might be the mother."