I'm fairly sure that all of the old disk has been formatted since Nero was on it, and the new one--with the W7 OS--has never seen it.
I just don't have the time to learn the deeper aspects of the OS, so I'm not sure if it has some enhanced de-fragging going on. I gather one does not have to do this as much as the old days, so maybe it's house-keeping. However, the disparity between reads and writes belies this.