Special to the Director's Cut Blog By Gary Levin, USA TODAY The increasing usage of digital video recorders, which easily allow viewers to postpone viewing of their favorite shows, has vastly complicated the math of TV ratings, new Nielsen data shows. And it explains how ABC's Modern Family ultimately eclipsed Fox's American Idol among key young-adult audiences. In final season rankings out Monday (Nielsen's time-shifted rankings are delayed by about two weeks), Family, already one of TV's top shows, added an average of nearly 5 million viewers in the seven days after new Wednesday episodes aired against Idol. That's the biggest gain for any series, for a total of 16.7 million viewers. Among viewers ages 18 to 49, the comedy jumped 48% when factoring in delayed viewing, while Idol's performance show gained just 17%. But viewers rarely delay reality shows, news, awards telecasts and sports programming by more than a day. Sitcoms and dramas are most pr...