Quote Originally Posted by Errorname View Post
You have people who independently made their own shelters like the Brotherhood or House, but you also have more rural regions that weren't directly hit by the bombs. Like a lot of the early game towns in New Vegas are pretty directly taken from real towns in the region, and Doc Mitchell being from a vault makes him unusual in Goodsprings.
I'm not sure how much we can/should extrapolate from New Vegas. As I recall, Mr. House had a moderately effective anti-missile system installed, which shot down a lot of the nukes headed for the area. That would have allowed for a lot more of the non-sheltered settlements to survive.