what 8iron said is exactly correct. With it mainly being used to pull loads, it is expected that the truck will likely be running at elevated rpm's for extended periods. Ford wanted the engine to be able to handle this type of abuse. Also, with Ford having the idea in mind that most of the F-250 6.2L trucks would probably be company fleet trucks, they want to make sure they would last...regardless of the abuse the driver gave it.

I use to be provided a company vehicle for work/personal use, and even I had the tendency to ride it hard and hang it up wet. That is just the nature of how a company vehicle ends up being treated, since the drive does not have any ownership of the vehicle and doesn't care about getting 2mpg having a company gas card.