[ksa8907]

If they build it strong enough to actually pull 300,000 lbs (not terribly difficult) then they're covered. You'll never be able to actually put that kind of weight on a road and be dumb enough to use a pickup truck.

In effect, the limit becomes DOT regulations and local laws.

Edit:
Also, a lot of 2500 and 3500 owners get themselves in trouble by not using the lower of all ratings or by being heavier than the non-cdl limit. So, some trucks are already into this issue and the "ratings" are essentially meaningless for 99% of truck owners.