But once DRM is on the content, the license is basically checked when ever you want to play it and it might be said "no, you are no more allowed to listen to this piece of music", where the reason might either be that the company who sold you the music is bankrupt or they want to sell it again. This problem does not only exist for music but for videos, too. With the new "copy-protection" used on blue-ray and hd-dvd it is possible to say "no, this player is not allowed to play me" and "no, you are not allowed to use the digital out to play the soundtrack of that movie" for the simple sake of "a user could make a copy of it".
So basically the DRM is used to allow the companys to control what the user does with media he bought and it is even possible to revoke the rights you should have gained by buying a product.
Simply said: the user is no longer in control of his data and where he is allowed to use things in which way.