I don't wear a helmet solely for protection from head injury. I use it primarily to make myself more visible to other motorists by wearing a white full-face and have added some reflective tape as well.
A helmet also is for comfort, to keep june bugs and bumble bees from colliding directly with my face as well as rain and to extend my riding season greatly. I just don't see too many helmetless riders when the temps drop below 60F. Most of that crowd don't ride when it drops below 80F.
I guess what I'm trying to say is that wearing a helmet for protection from head injury is just a small part of what a helmet can do for you.