They don't have too! In that situation when the ball is placed on the 25, the nose on the 15 yard line is a 1st down. Since it was an exact spot (similar to a touchback) you don't have ot bring out the chains in that situations. Again, it amazes me how many are quick to place a wager and slow to know the rules here. The spot had the ball squarely on the 15, when the exact spot started on the 25, any of the ball on the 15 is a first down.
And back to the spot, barrett has the ball in his chest and the ball while in his chest reaches the linemans back which is over the 15. The spot was fair. I have no idea on the bad calls mentioned in this thread because I was flipping games.