The number of plies in the sidewall isn't the only important thing, the "thickness of the plies is as well.
Most off road tyres suitable for off road use will have two plies of 1500 denier (denier being a unit of measurement). BFGs have three plies of 1000 denier, so they are really only the same "overall thickness" in the sidewall as most quality tyres, but their marketing dept. gets a bit of help.
GoodYear MT/Rs normally have three 1500 denier plies, so they really have the "thickest" walls, but Cooper, with the new STTs has two 1500 denier plies, with a third 1000 denier ply angled at 8 degrees to they other two to stop tearing.....think about it.
Unfortunately, the staff at tyre retailers today don't get the oportunity to gain much product knowledge.......so most will tell you that the ove is BS (esp BFG dealers)......but it isn't.