I get all that. My argument remains the same. I am willing to bet that my Tundra at 9,999 lbs passes that test in shorter distances than a Prevost motorhome or a Kenworth dump truck. SAFETY... right? Well if the Tundra can stop faster, that would be safer wouldn't it?
The key here is "a manufacturer may limit the GVWR if so desired". Toyota has to worry about safety... but they also worry about reputation and warranty work. Maybe the Tundra can safely carry the 8200 lbs that the axles are rated at... but maybe that will lead to the potential for higher warranty claims. In order to keep their reputation for reliability and to reduce their burden for warranty work, they decide to be ultra conservative with their numbers to prevent quicker wear and tear.
None of this has anything to do with SAFETY... which is the word that is thrown out by people who drive (and sometimes overload) higher GVWR trucks. I feel that argument is null and void.