Which seems like a strange addition to make, and an even stranger change to leave out of the patch notes. Personally, I have music turned off maybe 90% of the time-- while grinding, I'm usually listening to my own music or watching a movie, and while raiding, I'm listening to my guildies on Teamspeak. While I like the Warcraft music as much as the next guy, I can only hear it so many times before I'm ready for something else.
But I supposed after the next patch comes on, I'll have to flip it back on again and have a listen. You have to wonder why they're spending time implementing new music when there seems like so much else to do, but maybe these are leftovers-- music written for Outland or other new content that Blizzard didn't have anywhere else to put.