There’s going to be some variance depending on how a person tends to listen to their music. I think the decline of CDs correlates pretty well with digital options being available, and people making the switch. There’s always going to be people at the head of the pack using the new thing and people that want to save costs by keeping what they’ve got. The accessory market affects that too, there was overlap when people would have portable digital music players, but still use optical disks for their home stereo and vehicles. But as manufacturers came out with solutions like iPod docks or Bluetooth streaming the digital devices were able to push out the physical media.