All these "industry changes" re tire pressure came about in reaction to the Ford Explorer tire fiasco, where Firestone took substantial blame for Ford's low-ball tire inflation recommendation. The same thing led to a federal requirement for a TPMS on every new passenger vehicle. About the same time, Toyo took a lot of heat over Toyo tire failures on Country Coach motorhomes, even though it was CC that had spec'ed under-sized tires. After that, Toyo refused to recommend any tire for a motorhome, regardless of brand.
With those two experiences in hand, the Tire & Rubber Manufacturers decided to place all future liability on the vehicle manufacturers. Then the RV manufacturer's lawyers quickly figured out that they must "recommend" for a worse case scenario to avoid any possibility of liability. And thus today they both refuse to acknowledge any other psi method or number.
Former owner of 2004 American Tradition
Home is in the Ocala Nat'l Forest near Ocala, FL