I'm not sure helmets can keep a person completely safe, but in my experience they help. I wear one all the time when riding because:
- In 1991 I hit a car that was illegally crossing a MUP in Denver and hit my head very hard on the concrete unhelmeted, and did not enjoy the resulting concussion
- In 2003 I had a hauntingly similar crash in a different city, and my head hit the asphalt equally hard - helmeted - and I had no concussion, which btw I did enjoy
However, I'm not ready to make a stand on whether helmets should be required or not. There are lots of examples, like yours 10 Wheels, where they are woefully unable to protect, but as in my case a lot of times they are. Just because of my own personal experience I will always wear one, but am not stating they will keep me perfectly safe - only partially.