Generations later, the family tree is so broad. We all have the same great grand parents but we don't associate with our distant cousins. It boils down to the fact the three bands you mentioned had more common influences while the next generation was heavily influenced specifically by these band's innovations.
There have always been guardians of cool but I think that everything is more fragmented than ever. I just find it funny when I see two kids arguing over whether or not the Ramones are punk or what sub genre from 2008 they fit into.