Fantastic Four: Rise of the Silver Surfer earned $57 million over the weekend dropping Ocean’s 13 to second place at the box office, but barely managed to squeak by its predecessor’s $56.1 million opening two years ago. The dark horse comedy Knocked Up stayed steady in third while last week’s other wide release, Nancy Drew, came in seventh earning a meager $7.1 million.

Industry analysts are still puzzled why recent blockbusters aren’t holding their audiences. Chris Aronson, senior vice president for ...