You have not provided evidence supporting your claim.
It has ZERO to do with climate and everything to do with State and Federal emission laws.
Parts of SoCal can get downright as nasty hot as AZ, yet you still get the 150K miles.
The single hottest and hellish location in the U.S. is Death Valley in CA. 150K mile warranty there.
Most of the milder climates are NOT CARB states and only get the 80K mile warranty.
In CARB states, it was 10/150K. In non-CARB, it was 8/80K - regardless of climate.
BTW... If I were to say "consistent everywhere" and then explicitly state that it's not the same everywhere, what would you think?
I found this:
State Matters - NGVAmerica
Sure doesn't look climate dependent to me.