A572 Domex weighs .284 Lbs per cubic inch. A36 mild steel weighs .283 Lbs per cubic inch... so they are virtually identical in weight.
A36 is ok I guess, but I have seen people bend outer rings that were made from 1/4" A36, not to mention they are more prone to coning when they are tightened. The A572 has virtually no coning whatsoever...
And, the materials run the same price for me... so there is not a good reason to use the inferior metal. Both can be welded with every common practice as well, so thats why I use the Domex.
It may be a while before the ranger gets a set. I have them on my jeep and they work great, but I don't need them on the ranger yet, and probably won't put any on it until its not my DD any more.