Diamond Gusset won't guarantee abrasion resistance, I'm guessing someone "tested" it out and found that it wasn't nearly as good as leather. That said, they have thick denim - good quality denim too, and Kevlar liner under the denim in strategic locations (hips and knees).
I swear by Diamond Gusset myself, they really do make good quality denim products - although I think they're becoming victims of the global market, as they pride themselves on being 100% American.