Not that what your saying is true... but once I got into a accident in Quebec city. the snow slid the car and the car started to twirl. I hit the sidewalk on the drivers side... flew out of the car (since some how the door opened) went into a snow bank and the car wrapped around a tree. the driver's side didn't exist anymore. So I guess if I had that belt on I would be dead.
But in general... you should keep it on.