So, after all this talk, I finally did have an accident over the weekend, where a helmet would have been really useful to avoid a painful bump on the head accompanied by roadrash. Unfortunately, I wasn't wearing one since I was walking at the time.
(I was in Home Depot, and someone had left some concrete reinforcement mesh laying flat on the ground, in an aisle where it wasn't supposed to be, and I was looking for something on the shelf rather than down at my feet, my foot got stuck in the mesh, and the rest is very embarrassing history...)
This doesn't prove anything at all, but I thought it was funny... I did wish I had been wearing my helmet, though!