The thing is American trucks are built for use on paved roads, I doubt 10% of them ever make it off pavement and then only occasionally.
If you go to parts of the world where trucks may never see pavement, the Toyota Landcruiser and Hilux is the truck of choice.
I've driven Fords in the oil fields where they live their lives on gravel roads and they are shook loose by 80k on the odometer.
We actually use our F350's quite a bit off pavement, pulling horse trailers and hauling round bales. No doubt the Toyota would be a better off-road pickup if you weren't pulling or hauling.
I have yet to see a Toyota that could lug 5-6 horses and a 20' gooseneck up some rutted up cow trail that passes for a road.
Most people have a 'heavy' work pickup and use an ATV of some kind for bombing around off-road.
You are correct on one thing, 100k miles is about the max before the pickup needs to be replaced.