The bullpen is simply amazing. Salas, Jeppy, Smith, Street, Morin, and Rasmus are all having the best seasons of their careers. I haven't done the math, but I assume the combined ERA of those guys (plus Grilli) us somewhere in the low 2.00s.
It is one thing to have a couple guys in your pen with low 2.00 ERAs, but quite another when it's all seven guys.