Manufacturing of a retreading is different than manufacturing of a tire from scratch. There is also a bond between dissimilar rubbers (the OEM case rubber and the retreading rubber).

Also, the "case" of a tire isn't necessary designed to last 20 years or 100k miles. Belts separate as tires get older.... just one of the common failures in "old" tires. I emplore you to carefully read the warranty PDF on the treadwright website.... you'll notice that ONLY their tread manufacturing is covered. If you get a set of their tires and one of the belts separates after 2 miles, you're SOL.