Here is Kubiak's position on it:
Let's face it, while there are differences between the two (Manning more cerebral and quicker release, and Osweiler more mobile and better arm), the offense is going to be largely the same between the two QBs. In the week 17 game, we saw Manning under center more. I'm not sure of the breakdown of shotgun vs. under center (I don't remember any pistol). So, I think there is really marginal difference between the QBs, because by and large, Kubiak is stubborn and is going to call "his" game regardless of which QB is in.On why he announced a starter rather than have the upcoming opponent prepare for two quarterbacks
“I’m not worried about that. I’m worried about my team and our guys knowing what we’re doing. They know exactly what we’re doing. Like I said, we’re just very excited about our opportunity and we know we’re going to have to play extremely well—a lot better than we played the other day—but that’s the way it should be this time of year. We’re looking forward to it.”