#7 by hanako - Mar 3 2013
The theme song was commissioned for this specifically. The rest are individually licensed for use from royalty-free providers (basically, I spend a lot of time trawling through music catalogs and paying for the tracks I want).
That does mean that sometimes there's a chance you'll hear the same track somewhere else, if someone else also pays for a license to the same piece. That's also why I can't sell game soundtracks. I have the right to use the music in a game, but not to resell it.