Exactly, it's all about limiting their liability.

Since a vehicle is designed to carry, or tow a certain weight, the manufacturers inflation specs. have to take that into account.

They know the average driver isn't going to be adjusting their tires inflation pressure, to accomodate varying loads. So they just recommend a pressure that will safely handle a fully loaded situation.

I run my LT265/75R 16 6 ply tires at 27 psi rear, and 31 psi front, on my 3rd gen. 4Runner, when it's just me in the vehicle. This results in even tread wear front and rear.

If I were towing, or loaded up with more weight, I would adjust the pressures accordingly.

 

Amazing how many cars you see with terrible inflation-induced tire wear ( usually from underinflation...) I check my tires more often than my oil. It's easier - you don't have to, like, open up the hood and feel around for the stupid dipstick....