After taking a few weeks off with an injured ankle, Cedric Peerman participated during every practice this week (on a limited basis), though was listed as questionable Friday afternoon.
However due to the importance of Sunday's game, we can only judge that questionable injury statuses tend side with a greater probability of activation, depending on the health at that player's respective position. Adam Jones is important as a third cornerback and punt returner, so it explains that. On the other hand, Josh Brown has beautifully replaced Mike Nugent, who is out this weekend.
Yet on offense the Bengals are short with running backs. Despite Dan Herron's performances on the punt return team, blocking and knocking blocker into the punter on another, he hasn't shown nor promised production on offense. Therefore he sat because Peerman is far more important to the offense and shown has a greater history of production on special teams (don't forget the fake punts).