It's everything stated plus one more big reason. 3/4 and 1 ton pickups have full floating rear axle, that hub you see sticking out the center of the wheel. 1/2 tons have a C clip rear end. The difference? If you break an axle with a C clip rear end your wheel and broken axle can exit the axle housing, typically your truck and trailer will end up in a wad of bent/twisted steel. With a full floating axle you just lose forward drive, gentle braking will bring you to a stop in one piece.
One precaution for 3/4 tons, every once in a while manufactures come out with a light duty 3/4 ton. What they really are is a heavy duty half ton and not a true 3/4 ton. Not a lot of them out there from what I've seen because they never sell well.