Well, since everyone seems to think their one ton truck is a semi tractor, I can see why they would decide to put something slightly closer to adequate brakes on them.  Brake performance is pretty much always limited by the room inside the wheel to put the rotors in, so I can understand why the larger rim size came to be.....not that 17 or 18 are really "new-fangled" sizes....we had an old pickup here when I was a kid with 17" on it, and I recall a pair of 18" split rims laying around as well.  I would have preferred that they'd used 17.5, though, because then there would be some decent casings availible.  Big lug mud tires are no problem...Bandag, Michelin, Goodyear, Oliver, and whoever else is in the cap business has the tread....but light truck casings are not really strong enough to hang that much tread weight on unless you keep them at tractor speeds.  We've done it in the past on 235/85R16s and it worked decent as long as you used a G159 or equivilent commercial casing but it doesn't work so well on Light truck casings.