It's possible that having just started the season has an effect that diminishes as the season progresses, although with there being similar numbers of teams that finish seasons as much above the overall season leader, that downward slope likely isn't there.
I just went back and looked at three sets of stats from 2012: Red zone percentage, # of red zone touchdowns scored, and overall offensive touchdowns scored.
There was -- unsurprisingly -- a great deal of overlap between the top 10 teams in each category.
Of the top 10 teams in the number of red zone touchdowns scored per game, seven of them were top 10 in red zone percentage for the season.
Similarly, of the top 10 teams in overall touchdowns scored per game, seven of them were top 10 in red zone percentage.
The three teams exempt from each list were different, by the way, which I found interesting.
Anyway, what this suggests is that the teams that convert red zone possessions into red zone touchdowns at a high rate are the ones that score the most touchdowns. Not just red zone touchdowns, but overall touchdowns. Essentially what it suggests is that most touchdowns are scored from the red zone. And what that suggests is that red zone possessions themselves are not a random event. They're either functionally uniform across the league or correlated to the teams that can convert them into touchdowns at a high %.
Whichever it is, it appears that if you have a high red zone percentage, chances are you are scoring a lot of touchdowns regardless of other variables, which would contradict my earlier point that we need to be focused on moving the ball more consistently to create more red zone chances. As long as our percentage stays up, it doesn't seem to matter.