No, it's not just a sunny climate rule. However, it
is a generalization. Your tires may last more than seven years, but the odds are they will not and why drive with the fear of a blow out in a large heavy rig. Sign up for the Michelin Tire Program it will save you a lot of money when purchasing new tires. You can sign up through the FMCA. Link below:
Tire Connection - Michelin Advantage Program