I work in a practice that specialise in RTA accidents, we defend 99% of our cases and believe me. Car v Cycle. Not pretty, i've seen pictures ! And it's not the head that gets injured in a cycle/car accident, it's usually from the waist down i find. It's really horrific.
That's what gets me, there is all this moaning about "cyclists should always wear a helmet when riding on the road". Well I honestly believe that the road is one of the least needed place for a helmet.
You fall off on a road it's usually because you have been hit by a car and as you said most injuries aren't going to be helped with a helmet. On the other hand fall off on a cycle track or out in the woods and most of the injuries (getting rid of scratches) will probably be bumps to the head. Yes wear a helmet to be safe on the road but don't go out in your skin tight lycra at the same time, and don't even contemplate telling others off for not wearing a helmet on the road...
Top tip for cyclists ( which will probably enrage some car drivers on here), as already mentioned, protect your space. Cycle between half to 1m away from the pavement, that way if a stupid car driver gets too close you can make some space between you and them by going closer to the pavement, you can't if you're in the gutter.
I believe that there should be a compulsary, say 20 hours of road cycling/horse riding included within driving tests. It may be an annoyance to some but it would vastly increase the awareness of a lot of car drivers to other road users (motoryclists, cyclists, horses and others) that have just as much right to be on the road as you.
I cycle, but try and obey the rules of the road as much as I can, with the exception of the occasional red light as due to the brilliant way Plymouth has set up their motion sensors on the traffic lights if I don't go through them I would end up waiting forever (quite a lot of them don't seem to be able to sense cyclists coming up to them
)