I haven't been in any accidents as bad as ones being described here, but a policeman told me seatbelts prevented any injury that might have occurred in an accident I was involved in. I am more comfortable wearing a seatbelt, than driving without one. Also, while I have no fear of flying, I usually keep my seatbelt fastened for the duration of the flight.
What makes less sense to me than not buckling up, is riding a motorcycle without a helmet.