I can only hope they go in the same direction as Google Play Music - offer free cloud storage for your own music, with a paid "All Access" upgrade for unlimited streaming of everything.
Spotify is not "just a streaming Internet radio service". It does everything Xbox Music does. In fact, I am listening to my cloud-based collection on Spotify (free) right now.
I like to be able to type with my MacBook Air on my lap. It doesn't look you can do that with a Surface - it requires a kickstand to be placed on a table, right? The Air wins.
I never used Zune, but I will say that Xbox Music is sorely lacking in features compared to Spotify, Google Play, and Rdio. I don't know why anyone would choose Xbox Music over those services.
I love the auto-upload feature, but it for some reason it drains the battery on my Nexus 4.