Great point.
I generally hate DRM, unless as you say, the process really fits a service model.
Zune has since moved away from DRM when you buy music - they now generally give you unprotected MP3s. But if you get a subscription it really is a service - you can download all the music you want but it will expire if you don't keep up the subscription (although you do get to keep 10 songs a month in MP3).
I think that model of DRM is the only one that I've seen that actually seems fair and works.