[Mr. Adventure]

It's very possible you're right, of course, but I won't be convinced until I see that they stock different part numbers for the brake parts for the same vehicle with different engines and therefore different tow ratings. When they figure this stuff for weight ratings, it's not just safety. It's also marketing, durability and warranties that are parts of the equation, hence the higher ratings for more engine power.

Think about it: stopping is road, tires, antilock braking sensors/software/hardware, and of course the common brake wear parts. What manufacturer would want to defend a personal injury claim if there was a perfectly compatible set of brake parts in the product line that's 30% better, costs them about the same, but which they decided not to use? How about the liabilities in a different case where some dealer puts the 6000# rated pads on the vehicle that needed the 8000# pads because they didn't notice some option group that went with the engine number (or happened to be out of the right ones, and these happened to fit)?

I'd bet that manufacturers use the same brakes in most versions of the same vehicle as much as they can, just to avoid these hassles and the extra part numbers to engineer, manufacture, and stock.