Fox‘s “American Idol” has fallen to No. 2 on Advertising Age’s annual list of shows with the highest ad rates. The average cost of a 30-second spot on the Wednesday night edition of “Idol” has fallen by a full third, to $340,825. That puts its ad price behind that of football. It may have something to do with the fact that the franchise's ratings are falling faster than Felix Baumgartner on a flying futon. Come to think of it, maybe they should do the show from a dirigible.