Aceves pitched the most innings out of anyone in that bullpen.
The point is, that with the returning cast, Melancon (who hasn't looked good) and Bailey (who has a minor thumb injury, call the ICU unit) don't have to be lights-out to keep the bullpen respectable.
Also, i bet you would have complained if they kept Papelbon at that money if he reverted to 2010 form. It's just a lose-lose proposition.