Any one who has seen BB coach for any amount of time, knows that he goes out of his way to NOT run up the score, unlike say Tony Dungy.
He wants to win comfortably, and would rather run the clock with a run game when he has the lead, rather than take chances and try to roll it up.
He wants to train his players in playing with POISE in tight situations. You will have those situations against good clubs in the playoffs. You need to practice to excel in such situations.
He does not want to provide any ammunition for the next time he faces the opponent by rubbing it in. BB thinks ahead.
That's why the Pats will not cover the 16.5 UNLESS the Bills absolutely lay down. The Pats will probably rush for 250 yards. More probably, a 24-10 score is more likely.