Super-hero blockbuster sequel "Iron Man 3" stayed on top at the US box office after it's mega debut a week earlier -- but "The Great Gatsby" was also a power player, industry estimates showed Sunday. On its second weekend in US theaters, "Iron Man 3," starring Robert Downey Jr as the title character, took in $72.5 million, according to industry tracker Exhibitor Relations. Added to its take since… More...