You're right, but OGR's and shrubs don't require grafting and were rarely grafted even when all hybrid teas and floribundas were grafted.
It can make a difference even in shrubs, however. My Kordes fairytale roses (shrubs) from Palatine, which are grafted, are veritable giants, but the own-root nurseries selling them estimate their height at 2-3 feet, and my grafted Austins and Bucks are much larger and healthier than all of the own-root ones I've bought from Chamblee's and Roses Unlimited.