There is one other consideration on why springs on the fronts and not on the rear. I'm assuming (that alone could get me in trouble) Lance took the view that the flexing of the rear bumper was enough to take any loading disparity on the rears.
I'm thinking they had the turnbuckle thing all wrong as there is a lot more weight on the front turnbuckles than the rear and that end should remain with the truck bed and frame at that location. That's why i loosen the rears when off-road to allow the lighter rear on either side the freedom to lift off keeping the structural integrity of the TC intact for one more day and not follow the flexing of the frame.
jefe