I don't quite see how digital and physical music equate in that same way. Quality differences aside, a lot of digital stuff comes packed with a DRM or other securities disallowing a back up to another source. For example, the minute my old sony MP3 player breaks , I can't take the music I purchased online from Sony for it and put it on my brand new iPod. Even if I backup, it is a fail. The average person doesn't even realize what is sometimes encoded into their music and video when they purchase, and a lot of places are not upfront on whether or not they encode a DRM into it.
In the case of the iPod, there is no first party option to back up your music at all, at least last time I checked. I haven't used any of the new iPods, but on mine you can only pull off your music by downloading a 3rd party utility that will export the music from the iPod, and depending on what the music tag says, it will alter the naming scheme in the process. A lot of people also have been aggravated by the Sync function on itunes. If they lose their music on their computer, many people naturally plug in their iPod to see if they can retrieve it. Well, if they didn't turn off Sync in iTunes they will be rudely surprised that their music lacking iTunes automatically synced their iPod with it, aka: erased all the music on the iPod without warning because there was no music in iTunes.
Also, backing up is a risk itself. A few years back, I was backing up my hard drive to an external drive I had set up as a backup. During the transfer process, both my drives because corrupt. I don't know if it was a power surge or virus what, when I came back I found I had two corrupted hard drives. Legal documents, projects, artwork, photos. I am glad I was savvy enough to get back some of it, but I lost a lot of stuff.
More recently, I resolved to backup my music on the Google play. After two weeks of straight bandwidth usage and stalled up internet, I finally uploaded most of my music. Talk about a complete pain. I have a feeling that getting it back would be the same kind of hassle.