I remember reading about that, although this is only with regards to potential accidents involving a car passing you, which is only a tiny fraction of reasons as to why you could fall off your bike and hit your head.
No matter what you're doing on your bike, you could fall and hit your head and die. You could fatally hit your head repairing a puncture (insanely unlikely but not impossible) you should wear your helmet when you think the chances of you falling and hitting your head become greater than the sum of your reasons not to wear one. The problem is is that people don't value their safety enough over 'looking cool' and all the other reasons not to wear a helmet.
However because it is only yourself you're putting at harm and it in no way can harm anyone else, it should be up to the rider to decide, not the government.