For starters, in case you haven't seen it, Reddit posted a pretty damn interesting chart that illustrates the circular nature of NFL wins in 2010. It's certainly worth a look, and judging by the title text, it's meant to illustrate the level of parity present in the league right now.
In a sense, it's relevant to that argument, as it convincingly demonstrates the idea that any given team can win on any given Sunday. From a long-term perspective, though, most of us know that this is misleading, and that the title of this here post is a comically obvious statement.
After the jump, please see a chart that assesses the level of NFL parity from a different, long-term perspective.
Only 18 of the 32 teams in the league have won a Super Bowl. This statistic is a bit skewed, because a) the NFL tends to foster championship-hogging dynasties, and b) some teams have been around a lot longer than others, so I used a different metric.
To come within spitting distance of even reaching a Super Bowl, a team must win a game in the postseason, so I simply counted how long it has been since each team won a playoff game. Seven teams won in the postseason last year. The Bengals, on the other hand, are 20 years removed from their most recent playoff win.
What does this mean? Well, in the NFL's playoff format, anywhere from four to eight teams can win a game in any given postseason, so let's take the average -- six -- and divide the number of teams in the NFL (32) by this. Using this rather rudimentary math, if there were perfect parity in the league, no team would be more than five or six (to be more precise, 5.3) years removed from its last winning season.
We have 13 teams that go above five, and 11 that go above six. That's between a 35% and 40% deviation from what, using the criteria I've laid out, would resemble perfect parity. Any fan of the Chiefs or Bengals, for example, will tell you that reaching the playoffs can be miles away from actually winning a playoff game. Winning in the NFL postseason is hard as hell to do, and nearly half the league bears testament to this.