Someone better say: yes you need to own your music to listen to it offline! If you don't like that you can go and enjoy live music. Imagine that! A music fan actually and directly supporting music they enjoy.
Don't let Spotify or Rdio or any streaming service be "THE" way you access music. They are simply versions of a very large commercial
Muzak like catalog which (for a significant investment) only lets you save a temporary playlist without ever getting into a relationship with any music. You are accessing a money stream set up by lawyers and extracted from the artists. Really, is that the way to support music?
Support the artists. Buy their music. Own it, proudly, and stream it to whatever device as many times as you wish, without any cost, because you own it.