You bring up a very good point, and obviously no, your wife is not sexist. However, your point is one of a person's interest in a particular field. What influences a person's interest? If you have young boys who are constantly told going into certain fields of study make you "less of a real man", young girls who are steered away from certain fields because "that's not what ladies do"...coupled with outside influence from the other kids, adults, the media, TV, the internet...for most people, they will pick the path of least resistance.