If Bruce Springsteen ever played the D.C. area on September 11, it’s not hard to imagine that it would entail a long, workmanlike set of earnestly anthemic music, plenty of emotional catharsis, and at least a handful of politically-engaged soliloquies between songs. For better or worse, local concert-goers were denied that spectacle this year. Instead, they got Vampire Weekend, the much-hyped indie-rock band that, coincidentally, vowed at a 2008 9:30 Club show to return with enough new material to fuel a marathon set worthy of “The Boss.” Despite having since released a new album, Contra, the NYC-based quartet didn’t quite manage that feat at their show at Constitution Hall earlier this year, nor at Saturday night’s not-quite-sold-out concert at Merriweather Post Pavilion, where adoring fans had to settle for an enjoyable 75-minute performance that included, fittingly, a mid-set cover of Springsteen’s “I’m Goin’ Down.” Singer/guitarist Ezra Koenig kept his banter light, affable, witty, and apolitical, and his band’s music struck similar tones, demonstrating that Vampire Weekend proudly carries the time-honored torch of pop escapism.