look at the videos again. foster is directly over molina's head not his left shoulder. the camera angle just makes it look that way.
hirshbeck stays in the slot, he just moves it and himself with the catcher. the slot is that area on the inside part of the plate, between the catcher and batter that affords the umpire with the best view of the entire plate. by moving out with the catcher you are still protected unless for some reason the pitcher can't hit that outside spot.