Vic-I bet there is some logic to the type of surface affecting tire wear. I've noticed I get a little different mileage on tires on different bikes that are used on different surfaces and they are the same type of tire.

Good point on checking the sidewalls and beads. I had just finished a really fast downhill and had a tire to blow out on the sidewall. It was actually a wired bead and apparently there was a weak spot and the sidewall came off the bead and the tube blew. Just glad it didn't happen when I was doing 40+ down the hill.........plus I never bought that type of tire again.