iTunes doesn’t include live individual American Idol performances or recordings in its weekly chart of the most downloaded songs, but if the online music retailer did, the Idols would likely be landing near the top. Just consider the artists they’ve covered: After David Cook name-checked Chris Cornell’s version of “Billie Jean,” sales jumped from 224 to 14,861 weekly downloads, while Jeff Buckley’s “Hallelujah,” sung by Jason Castro, shot to the top of the charts with sales of 174,553. As for video performances, after April 9’s Idol Gives Back, six clips hit the top 10, including the Idols’ opening number cover of Rihanna’s “Don’t Stop the Music,” which went all the way to No. 1, beating new videos by Madonna and Mariah Carey. Apple’s iTunes store was recently named the top music retailer in the country, surpassing Wal-Mart for the first time. Could Idol be the reason why?