It's a tragic story (if it isn't viral marketing for the car seat; sorry to be cynical but a quick search indicates that the only ones saying seatbelt failure is common are PI lawyers).
Obviously I'm not a parent so it might all change if I were to become one, but this is true on other topics as well: You take reasonable precautions and sometimes **** happens. Reducing risk to zero is a fool's chase and most people suck at honestly evaluating risk and spend huge amounts of time, money, and worry avoiding relatively small risks while walking right into much larger ones.
Ran into
this thread about the video at car-seat.org. Post #15, particularly, is of some interest (and the whole thread lays to rest the viral marketing concern).