I have the same experience and nearly the same advice, FWIW.
I believe that roses produce and release into the soil growth inhibitors. A large, well established rose might leave behind some of these and retard growth of a new rose. I do usually try to mix in at least 50% new soil - mostly soil ammendments. But even this it may not be necessary if the previous rose was not large and well established and if the soil is fertile, loose, and moderately water retentive.