While the appealing, simple answer is a catching problem, that's a gross oversimplification. Criticizing officials usually comes off as petty and prejudicial, but is anybody watching?
Missed strikes have massive, often imponderable consequences. Often an error or a defensive miscue (such as the Angels' misplays by both Hunter and Bourjos last night, can trigger not only a rally, but higher pitch counts and longer innings. Last night Jon Lester (not Saltalamacchia) got repeatedly 'squeezed' by Larry Vanover. My sense was that Lester wasn't getting the low strike. As a result, Lester had a much higher pitch count early, which taxes the bullpen, and triggers a cascade of consequences.
Over the longer haul, the wear and tear on both the starters and the bullpen has meaning. The biggest meaning is more frequent appearances for the perceived 'reliable' relievers.