@George,
The NFL was the "original" league, run by a bunch of rich white guys. The AFL was an upstart group of other rich white guys who wanted to get in on the action. Eventually they merged. The divisions (N S E W) were set up based not on geography but on the intensity of the rivalry (Baltimore and Pittsburgh or Washington and Dallas, for example). You can see that manifested here in some of the picks people make.
Teams in a division play each other twice per season. Most of their other games are within their conference but they do have the odd game outside their conference so that fans can see a matchup they normally would not see.
George correctly observed that the whole thing is set up to build to the playoffs leading to the Super Bowl.