My wife rolled a car several times. The only injuries she suffered were a burnt, swollen face and black eye from the airbag, and a broken collar bone from the seatbelt. Could she have been ejected from the car and killed without it? Quite possibly. Could she have been unharmed without them? Quite possibly as well.
I posted this as sort of a joke, but I guess I'm the only one who thought the title of the story was odd.
After reading the responses, my point is: How do you know a seatbelt saved a life? I do not believe anyone can state with any certainty the outcome of a crash with versus without.
I'm sure wearing a seatbelt is probably a good idea. After all, it's been beaten into your brain for years that it is, so it must be true.