Peyton didn't develop this skill on his own he got help. Bet if Peyton had a young qb like luck and taught him everything he knew it would work.
The problem is Peyton would never work with a young QB/Teammates--like Luck--to teach him as long as he was the starter.
Manning was notoriously selfish about taking all /the lions share of snaps during the week, and was known not to work with or teach back ups. That's just how he was. It was all about him. And he makes no apologies for it.
Would this preclude him being a good teacher as a coach? I don't know. Probably so. Because people who like to teach usually have that bug in them. And Peyton hasn't demonstrated the sharing/empathy quotient through out his career.