You gotta keep in mind that pulling that much weight on wheels is a whole lot different that pulling that much weight being a log or a sled on the ground. That's a lot of friction to deal with. Most every one I know can push a vehicle out of the road when it quits.
i agree it is different. they still got to be some stout mofos to pull that much. I figure if they could pull that they can pull a little ole hog out of the woods if you trained them for it.