Look at the picture from the Tpub. You can see the design difference there.
I think there is a thickness difference.
On my truck, I regularly run my tires at 45-50 psi. I trailer and haul loads in the bed. I played with tire pressures and found 45 to be about the best for me(temp, wear, contact, sidewall flex).
I would hate to have someone read the sidewall max pressure and think they were safe to inflate to that , if my tires were on the 8 bolt rims.