?? While you pay monthly to be a part of emusic, you download mp3s and own them forever. This is not a subscription service model as this topic relates to. I think this is about the subscription services where you stop paying and your songs stop working...
The argument could be made that either model could meet the requirements of matching the broad term, "subscription".
Essentially, I look at an eMusic subscription in much the same way as I'd look at newspaper subscriptions. If I cancel my newspaper subscription, the papers that have been delivered to my house up to this point don't all suddenly disappear.
Then there's the Rhapsody subscription model, which is like a subscription to the IEEE standards library... While the subscription is in good standing, you can access anything in the library without any additional per-unit fees. Once the subscription runs out, you lose the legal right to use any material you'd amassed during the period of the subscription.
Finally there's the rental model (ala Blockbuster), which many readers here seem to have confused with either of the two subscription models above. In a rental model, you pay on a per-song basis, just like you would for purchases, except for two big differences: (1) The per-song fee is typically smaller than a purchase, and (2) You can only listen to the song a limited number of times, or for a limited timeframe, before the song becomes unusable and would have to be re-rented.
I personally think a subscription in the eMusic sense would be a very valuable addition to iTunes. I also think a rental model in the Blockbuster sense would be nice for movies. I'm not convinced that a subscription in the Rhapsody sense would be good for anybody.