According to the latest data released by The NPD Group, iTunes now represents a quarter—25%—of all retail music sales in the United States, more than ten percent more than its closest competitor. Based on all music sold in the first half of 2009, iTunes sold 25 percent of it, up from 21 percent in 2008 and 14 percent in 2007. Walmart, which sells music through its brick-and-mortar stores, Walmart.com, and its Walmart Music Downloads initiative,…
