Sucks for Peyton, but Why, Cowher?

The game I looked forward to all weekend long was the Colts-Steelers game. Poor Peyton, couldn't get props at the Heisman Awards (long live Michigan's Charles Woodson, who Tennessee Volunteer fans still hate as a result), can't beat the Patriots til 2005, now still can't win a playoff game. But I had to suffer through the Detroit Lions this season, so I don't feel sorry for him. But what I don't get is this: why did Steeler Coach Cowher try to run the ball instead of taking a knee when they had the lead with just over a minute to go? They could've run the clock out with less than four downs, since the play clock is 45 seconds. A bit of rust on the iron jaw, perhaps?