The discrepancy was noted over at Mac Network News, which has posted screen shots of Apple's 10 million song claim. The iTunes music inventory inflation appeared in a note that Apple sent to iTunes customers last week announcing that iTunes was 5 years old.
Apple did not respond to a request for comment.
Apple currently says that 6 million songs are available through iTunes, the number officially cited in Apple marketing material back through September 2007.
"The iTunes Store is the world's most popular online music, TV, and movie store with a catalog of over six million songs, 600 TV shows, and over 1,500 films, including 200 in stunning high definition video," Apple said on May 1.
In an Aug. 14, 2007, press release, Apple said it offered more than 5 million songs through iTunes.
Amazon.com in January said it sold more than 4.9 million songs through its competing MP3 Download service. According to an April article in The Wall Street Journal, Deutsche Bank analyst Jeetil Patel estimated that Amazon's digital media initiatives have produced less than $100 million in annual revenue, despite $300 million in investment over three years.
In early April, Apple said that according to data provided by the NPD Group, it had surpassed Wal-Mart as the leading music retailer in the United States. It said that it has sold more than 4 billion songs through iTunes worldwide, in the five years of its existence.
In February, an NPD Group report said that Apple's iTunes Store was selling 10 times as many MP3 songs as Amazon's MP3 Downloads service.