iTunes for Win - why?

So there is some hub-bub that Apple is going to announce a version of iTunes for Windows this Thursday. While I think it will be quite interesting to see what Apple designs for a PC application, I can't help but wonder if the service will actually go anywhere. Are people not joining these services because they are too difficult to use? Too much of a hassle? Not enough selection? Or is it because they have a free alternative? I'm skeptical.. why choose iTunes over BuyMusic? or the new Napster?