Apple excitedly announced Wednesday that it had sold its 10 billionth song on iTunes. Maybe a little too excitedly, because the notorious perfectionists at the company spewed a typo onto its home page. The iTunes Store has been active since 2003. It recorded its first billion songs in 2006, and 5 billion by 2008. While beginning with music, it has gradually expanded to include movies, TV shows, games and applications. The company is meanwhile highlighting a list of all-time bestselling singles, predominantly controlled by recent mass-market acts like the Black Eyed Peas, Lady GaGa and Katy Perry. Topping the chart is the Peas’ “I Gotta Feeling.” The rankings may be dictated less by genuine popularity than the coincidence of certain songs’ debuts with the growth of iTunes, the iPod and the iPhone.