I'm really not sure why some of the other comments here are focusing on the playing of music on the stream. Obviously they've never watched someone gaming on twitch. Nobody watches twitch for the music someone is playing. People watch it to see other people play and talk about games. Music may be in the background but is often obscured by dialog and game sounds. It's not even close to the quality a youtube video for music supplies.
Music isn't obviously not the focus of any Twitch stream, but nevertheless, people are breaking copyright laws by playing copyrighted music on their streams. And if Twitch becomes a part of YouTube, they might have to crack down on copyrighted music on streams, due to pressure from the copyright holders.
Moving away from the music for a second, the public streaming of gameplay doesn't constitute copyright infringement? I'm no legal expert but it seems to me a bit of a stretch to call it fair use - especially for single player games.
Music is a good differentiation between streams. When I used to watch a lot of LoL streams that was one of my deciding factors on who to watch. Why watch someone playing all top 40 stuff when there's someone else playing music I enjoy?
