As an Australian I've spent my entire life wearing seatbelts. It's second nature. I don't even think about it. Taxis or otherwise. In fact I think it's required in all cases.
But in the US people seem to view the choice to turn a mild car accident into a severe or even fatal one as some kind of moral stance or personal freedom. Or rather any effort to require their use as Big Government or the Nanny State.
Some states still don't require rear passengers to wear seatbelts. [1]
Personally I wear a seatbelt in cabs and don't think twice about it. I'd feel uncomfortable without one.
Anyway, sad news.
[1] http://en.m.wikipedia.org/wiki/Seat_belt_legislation_in_the_...