LOS ANGELES — A sci-fi love story has given way to an earthbound romance at the box office, livening up typically slow times at theaters over Super Bowl weekend. Released by Sony's Screen Gems banner, "Dear John" debuted as the No. 1 movie with $32.4 million, knocking off "Avatar" after seven weekends in first place, according to studio estimates Sunday. "It is very cool to know that it was our movie that audiences just totally embraced and made No.