Do not forget that bike helmets increase the SIZE of your HEAD, which makes is substantially more likely that your head will hit the ground in the first place.

What about all of those cyclist involved in crashes where their heads missed the ground completely by an inch or so? They would have zero injuries to their heads as compared to if their helmet smacked the ground with their heads in them. Do they get counted in statistics? Do they say "I would have surely sustained brain damage had I been were wearing a helmet"?

(I wear a bike helmet BTW, just not for crash safety concerns).