The human body exerts force on the belts as a result of G-forces produced in an accident. These G-forces may exceed what the the person may survive, but the driver HAS to be restrained inside of the protective structure of the car. That is his best chance of surviving.

A report on the Scotty Kallita accident states that he was restrained in the car throughout the incident. "Multiple impacts produced G-forces exceeding 100G, with some approaching or exceeding 200G."
Cause of death was multiple blunt force trauma. There are unsurvivable accidents, but the last thing we should want to see are videos on You Tube of a driver coming out of a car in any of these incidents.

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Yes the MAJOR factor is to keep the person inside
of the car/cage and yes there are times that the G
force will just be too great for the body to withstand
and the person still dies.. thats just the way it
is (but at least they are still in the car).. I did
find the data interesting.. now I wonder why
the material fails in a 2 year period.. I would think
that the manufacturer can/could come up with a product
that will last 5 years.. or greater.. far as I know from some of the data that
I remember sunlight is the killer on many of the
nylon procducts but we do have enough technology and
materials to over come the sunlight issue... I havent said
this has been a money deal for the companies but if
they were to build a 5 year system and charge a bit
more.. then maybe we would all be happy..... JMO
EDIT
On the graft that someone posted from the SFI... with
that graft I would have been thrown out of a meeting..
it has to have numbers