«The iTunes Store has now crossed five billion song downloads, according to information confirmed by Apple.  The threshold comes more than five years after the initial launch of the service in late April of 2003, part of a mixed scorecard for paid downloads.  "iTunes is the number one music retailer in the US and features the largest music catalog with over eight million songs," Apple declared in a statement. 
Few would quarrel with those assertions, and iTunes still commands a dominant lead over its rivals.  That includes Amazon, blessed with DRM-free MP3s by major labels as part of a plan to ease Apple's dominance and market power.  Others, including Napster, have also been granted MP3-based catalogs.»

fonte: Digital MUsic News, The iTunes Store: Five Years, Five Billion Song Downloads , 19/06/08