LOS ANGELES (Reuters) - The "American Idol" finale audience slumped to a record low, but the show's newly crowned champion Phillip Phillips hit No.1 on iTunes on Thursday with his first single "Home." The 11-year-old Fox singing contest, once a TV industry juggernaut whose finale attracted more than 30 million viewers in 2006 and 2007, was watched by just 21.5 million viewers on Wednesday night, according to ratings data. Viewers in the 18-49 age group most-coveted by advertisers dropped by about 32 percent compared to last year's "Idol," although the program was still the top show on U.S. ...