NIN’s Creative Commons licensed Ghosts I-IV has been making lots of headlines these days.

First, there’s the critical acclaim and two Grammy nominations, which testify to the work’s strength as a musical piece. But what has got us really excited is how well the album has done with music fans. Aside from generating over $1.6 million in revenue for NIN in its first week, and hitting #1 on Billboard’s Electronic charts, Last.fm has the album ranked as the 4th-most-listened to album of the year, with over 5,222,525 scrobbles.

Even more exciting, however, is that Ghosts I-IV is ranked the best selling MP3 album of 2008 on Amazon’s MP3 store.

Take a moment and think about that.

NIN fans could have gone to any file sharing network to download the entire CC-BY-NC-SA album legally. Many did, and thousands will continue to do so. So why would fans bother buying files that were identical to the ones on the file sharing networks? One explanation is the convenience and ease of use of NIN and Amazon’s MP3 stores. But another is that fans understood that purchasing MP3s would directly support the music and career of a musician they liked.

The next time someone tries to convince you that releasing music under CC will cannibalize digital sales, remember that Ghosts I-IV broke that rule, and point them here.