Sometimes you just never know what causes a tire to go. I just felt the seven year mark was a good time for us (tires dated in '06 on our '08 Dynasty) and I'm sure we could have gone longer. We did use our coach monthly over the 7.5 yrs. that we have owned it putting on 69,700 miles. So, the new set of tires are 1.5 yrs. old with 11,000 miles on them.
The way it was explained on one of these threads is a tire is like a bowl of spaghetti with a good tomato sauce. If you don't use the tires the tomato sauce falls to the bottom. Using the tires and heating them up keeps the sauce mixed through-out the tire.
All this made total sense to me since I'm Italian. :p
MM.