MUSIC INDUSTRY: Artists Behind Oscar-Nominated Songs Won't Perform

Some of Oscar's most memorable moments have come during performances of nominated songs. Among them: rap group Three 6 Mafia surrounded by streetwalkers as they performed "It's Hard Out Here for a Pimp" from "Hustle and Flow" in 2006, and Celine Dion's resplendent performance of the "Titanic" hit, "My Heart Will Go On," in 1998...