5 Billion tracks / 175 Million ipods is just over 28, not 3. And since you can take your CDs and put those songs on the ipod, not all of the rest of the ipods are filled with pirated music.

Since my wife and kids got their ipods, the number of CDs that they buy has gone way up. They only use itunes when they want 1 or 2 tracks off of an album.