You think Manning isn't gearing up for a repeat, and I am not talking about Eli or the SB loss.
Out of the top 30 QBs in the preseason based on attempts only 4 are their teams unchallenged starter (EJ Manual, Peyton Manning, Alex Smith, Nick Foles) a few other like Bortles, Manziel and Bridgewater may end up being the starter but they are rookies so you would expect them to get the attempts.
Of those 4 Manual can be justified in leading the way because he is a 2nd year guy coming off an injury with something to prove and he needs the work plus they have to justify the Sammy Watson pick. KC has a woeful passing game even with Smith at the helm (or maybe it is because Smith is at the helm) so trying to build a rhythm with the receivers is justifiable and Philly is trying to figure out how to replace Jackson and prove that Foles was not a 1 year wonder so all three of them can be somewhat justified in playing a lot.
If any team was in a situation to have their starter not play at all and to give their backup a chance to prove what he has it was Denver. Manning does not need the reps and Denver needs to start planning for his retirement (granted Osweiler did have only 5 fewer attempts but he probably should have had 25 or 30 more)
So what happens? Of all the players and teams who had the least to lose and the most to gain from sitting throughout the preseason Peyton Manning is the only sure starter without good reason to be in the top 30 in passing attempts. This tells me that Denver, meaning Manning, is going to pass the ball and pass the ball a lot. He may not reach last years levels but if I am playing fantasy football I am ranking him as the #1 QB because if you want stat whoring Denver will be the place to be this year.