[Lynn Eades]

I think it's more a compromise where economics has won out over maximum tractive effort. the reality being that it's still going to perfom pretty well in all wheel drive.
How many times in the life of the tyres is a truck of that weight going to be floundering in mud,spinning all of it's wheels? ,and if iit was, would turning the two front tyres,on the rims, have seen it get through?
I'd say it's too fine a point, easily offset by the sure longer life of the tyres, as fitted. (and thats why they do it.)