I think a big part of it that a lot of you who don't mind high miles aren't thinking about is the resale down the road when you get rid of it. If you start off with a rig with 150k+ miles then use it for several years off roading and commuting, your residual when you go to sell will be a lot lower than if you started out with 30,40,50k fewer miles. I drive about 10k miles per year, so at this rate in 3 more years when I go to sell mine, I'll be just approaching 150k which should be FAR easier to sell and MUCH more appealing than a rig with 250k miles on it. For those who intend to keep their trucks forever and pass them down to kids or whatever that argument is irrelevant, but I think most here intend to sell at some point down the road where resale value will become an important factor to consider.
Just like real estate, the profit is made on the buy, not the sell...