I disagree. It's the ease that's important. If browsing the store is as easy or easier than purchasing and organising the music yourself, and you get to listen to almost every album ever made (in the west), then who would care about paying 10 dollars a month. People who like music spend more than that on CDs in a month anyway, so to be able to listen to millions of songs, and on multiple computers/devices (with "ease of use" being the absolute keyword) you would have to be a dedicated collector/ hoarder to not subscribe.
If this takes off in a big way for MC (and I hope it does), then they would even be able to stop charging for the software and make that a hidden part of the subscription charge too. It would be a cascading success. Free software with a killer music store would bring more people to the software and make it even more popular.
Of course, international distribution is the major hurdle. MC's user base it pretty international. I cant see JRiver negotiating music distribution rights on a per market basis, they just dont care about the store that much. So they need to make a one store for the world model workable somehow. I hope they do. They national boundaries on itunes music store really piss me off. Japan's itunes store's music sucks, is drm ridden, and is expensive. Without a foreign credit card I cant use any other store.