Originally Posted by JCL

That used to be more true than it is today. Older generations of snow tires relied primarily on the tread blocks on the edge (shoulder) for all of their traction. More recent designs use modern rubber compounds and much more sophisticated tread patterns to grip over the whole width of the tire. That is why we are seeing performance snow tires in these sizes.

You can't push down any more with a wide tire or a narrow tire. The narrow tire does have a shorter path for water to get squeezed out, reducing hydroplaning' as you say. However, since the truck weighs the same (lb) and the tire pressure is for all intents equal (lb/sq in) you will have the same contact area (sq in) whether you have a wide tire or a narrow one. All that will change is the shape of the contact patch, not the size of it (disregarding the effects of the sidewall stiffness).