In the 1980s it was the 49ers (Bill Walsh), Redskins (Joe Gibbs) and Giants (Bill Parcells) who were dominant, and most people can't even remember prominent AFC coaches and teams from that era.
The other problem -- at least in the 1980s -- is that the AFC often seemed to have very flawed, incomplete teams run through the playoffs. The Denver Broncos of the 1980s were very small on defense and had no real running game, so they were pushed around very easily by NFC East teams in two Super Bowls. I've often said that the Cleveland Browns would have been a much stronger opponent than the Broncos in those two Super Bowls -- simply because they played an NFC-type of game back then.
The Buffalo Bills team that lost four straight Super Bowls epitomized the flaws of those AFC teams. They had lots of talent and could beat anyone on any given day, but their "run & shoot" offense was a disaster at a time when a strong ground game that kept the opposing offense on the bench was a major weapon.
Parity comes from a lot of places. And coaching trees would certainly be one of them. We’re in our 3rd of 4th generation of coaches that believe in more than just execution, and most of the top end guys follow the family tree to the 1st generation. We really do have the Any Given Sunday league Rozelle dreamed about, a lot went into it, some stuff he didn’t even know would be necessary.