Helmets protect you. I slid down a street and my head bounced on the pavement - without a helmet I would have been much worse off. The road rash was enough. Another incident was a truck mirror that grazed my helmet. Nothing major, but in all, the helmet does its job.
I hope you aren't saying that seriously. If those vehicles caught bicyclists in the helmet, they were both just too close to the cyclists. What if the cyclist swerved an inch to avoid a rock in the road, or even simply turned his/her head to look at something? Yeah, whamo.
