In the heyday of "American Idol," the notion that it could fall ratings victim to a zombie slugfest or standard crime drama would have been laughable. That was then. With Fox's singing contest shedding about 20% of its audience so far this season to hit new lows, it's been leapfrogged repeatedly in total viewers by series including the CBS procedurals "Person of Interest" and "NCIS." In a harsher blow to a blockbuster that once ruled the advertiser-adored young adult segment, "American Idol" has been overtaken this season by...