A lot has changed in the last few years. Spotify gives me all the music I could ever want, and if something is missing you can sync music from Spotify on your computer to your phone, and everything is wireless. For video it's almost the same thing, YouTube and Netflix provides we with all the content I need to have on my phone.
"Cache" implies they're only temporarily on your device. This is false: the files are downloaded and encrypted on your device, and do not go away unless you explicitly tell Spotify/Rdio to remove them.
Spotify/Rdio will remove those files at any time if they lose the license to play them. This is not the case with media files you own, and have complete control over (lacking DRM).
Caching it on the device is enough for me. I'm fine with knowing that I don't really own my music, as long as I can still listen to it while I'm on the subway without cell signal.
