Torrentfreak explains in this post why most music artists profit from piracy even if global CD sales decline:

• 25% most popular artists sell less records whereas the remaining 75% sell more
• Music from most popular artist are available on p2p networks. It is easier for people to listen to those artist without buying their CD. Then they have more money to buy CD of less popular artist.
• Social service like Last.fm and Pandora allow to discover less popular artist.