The difference between subscription based mp3 clubs and purchasing mp3s is the different between watching cable and buying DVDs. And for the casual listener, subscription based music clubs are the future of music.
I buy tons of my music and if Itunes offered a subscription based PORTABLE mp3 rental service I would do so in a heartbeat.
Pandora is the FM radio of modern times, Itunes the Towering Inferno of mp3 sales. But subscription based song rentals is the future. For $15 you might get Itunes entire music catalogue. Something like 8 Million songs (around 50 years to listen to the lot). And itunes will do it soon.
Why?
Because the European, ad based, Spotify, are about to wake up to their having missed a golden opportunity to break open the States by refusing to go to pay to play based subscriptions in the States.
Apple have woken up in the nick of time that music subs is the future of recorded music.They are in talks and ready to launch in a matter of months.
A mixed blessing but better the devil you know i say.