the official word from Apple Canada is that the US is just in a "test phase" to see if the service will catch on. If so, Apple will proceed internationally.
If you ask me, I think it will flop on the windoze platform. There are more p2p networks, and i have noticed that windoze users are generally cheaper, and make less money. This is opinion is based on the clientele that i have seen at the computer store i work at.