Really? Which ones? Because I've ridden most of the B&Ms in the world and I can only think of a handful that are rough or have gotten rough over the years.
Case in point, we just rode Nemesis, built 16 years ago, Katun, built 10 years ago, Nemesis Inferno, built 7 years ago, and Black Mamba, built 4 years ago, and they were all equally as smooth as each other.
I don't know. Maybe its just me, but it seems that B&Ms are either super smooth or super rattly. For instance SCREAM at SFMM is a lot rougher than it used to be (in my opinion), and also some newer ones like Dominator (also in my opinion). Maybe its just me...