@Mark
You don't know, you're guessing. Fall off your bike (without helmet), assume the position while in-flight and walk away having narrowly avoided a nasty crack on the head. Doesn't prove that bike helmets are useless any more than your anecdote proves they're great.
Helmets are big and cause nasty cricked necks and suchlike in low-speed collisions instead of allowing narrow escapes and increased caution in future.
My 2p.