Doo's have always been known to wear down very fast in the front. Then they just get to a spot and wear very slowly. When you are down to the wear line and change them, cut them in half and see how much is left. There is a lot of slide left. Sounds to me like either a lot of people are riding on sand dunes, or they are just changing them waaaayyyy too soon.
I do not even bother to bend over and look at them until about 8000 miles. My son's sled will hit the 8000 mile mark in a few weeks, and I will bend over and check them, but I guarantee you that they are still just fine and have at least 2000 more miles on them.
And no, I do not "temper" them. I do not believe that makes one bit of difference.