Music is an emotional thing, the biggest difference between Rock and Rock'n'Roll is that they feel different. I know this explanation will not satisfy galacticsemen, but for any sensible human being you can feel the difference between them. Technically writing it may be difficult, but if you're in the mood for some Led Zeppelin or some Rush, listening to Chuck isn't going to satisfy you're craving. Sure rock is made of the same elements, but the attitude, the dynamic, the emotion, and the amount of aggression is all different. Something that can be much more easily felt than described.