Lew
Everything I've learned about tires over the years is exactly what you just said.
Additionally, rubber deteriorates naturally and I suspect that it has to do with the way synthetic rubber is made.
Synthetic rubber also does not get along well with steel tire belts and if the belts should get wet because of tire cracks, well, good luck. The cracks just allow more oxygen (ozone is a serious corrosive) and moisture to mix in the rubber.
Loren
