I think that is exactly why they haven't made a decision at QB yet. 

Neither Trevor or Paxton have really Wowed the staff and all they want is for one of them to step up. Trevor has consistently been winning the QB battle in camp and in his preseason play, but the staff still hasn't named him starter. Why? Because he has only been mediocre and not really stepping up. The fans see it the coaches see it.

If Paxton comes out and lights it up on Saturday, I guarantee you he will win the starting job. If not, Trevor will win by default. 

The Bronco's staff have given both of these QBs ample opportunity to take the bull by the horns and win the starting job. Unfortunately, neither player has done that.