Having a strong leader at quarterback doesn't mean that your team will make it to the Super Bowl, but without a strong leader at the position there's little chance of a trophy. Even on championship teams where the quarterback was hardly a statistical phenomenon- like the Baltimore Ravens of 2000-01- Trent Dilfer was still the undisputed leader of the offense and a true cog on the unit because of it. Perhaps that's one of the major reasons why the Chargers decided to part with Drew Brees. Philip Rivers simply appears to have the 'it' factor.
While Brees led the team and played well, it seems that Rivers was quietly laying the groundwork. He got to know the team and never seemed down. Though he always clearly wanted to play, Rivers never ruined team chemistry and stood behind the coach's decision to start Brees.