Let's talk about the increases/decreases, rather than absolutes (such as "teams have the same amount of money"):
1. Teams have closer to the same amount of money to work with, through revenue-sharing. At every step, revenue-sharing has decreased the differences between big-market and small-market teams.
2. It was under Rozelle that the League first understood the basic formula: We are all partners in one business venture, the NFL. So all the teams, for example, have to decide whether the Bills are allowed to give up on Buffalo... and if they're not, it falls on the league (at least in part), to "save" the Buffalo experiment.
3. As others have noted here, the better businesses will be more successful in use of more comparable resources. There is, in fact, a salary cap minimum as well as a maximum, to keep a Yankees/Devil Rays dichotomy from developing.
4. The perenniel winners do evolve from that difference in allocation of resources and yes, luck. But more to the point, there are fewer if any perenniel losers. Witness the Houston turnaround. Before that, the Saints. And before that, the Bungles. Going into the season, every team had a reason to hope. That's what's important, not that winners can not keep a winning edge, but that it is possible for the mighty to fall and the lowly to rise. That is very much the goal originally envisioned.
5. Are teams approaching the point of competitiveness week to week/season to season, or are they receding from that point? I believe they are still approaching that point.
It's a great subject for a Pats board, because we have been the fly in the parity ointment. We built a dynasty with a grand total of one, count him, one superstar. Add Seymour if you like, but this success story was really a Belichick/Kraft/Pioli/Brady combination.
Parity, in other words, can be mitigated by the right combination of coaching, personnel, and culture smarts. Notably, that's not saying you don't need luck/talent, as the Brady part of the equation illustrates.
But think about the coaching/business/personnel part of the Brady development.
They at least had a right hunch in the 6th round to pick him with #199... and you'll notice, it's a pattern. They're always looking for a Brady.
BB and company could look at that 2001 tape, watch Brady march the team down the field in clutch situation after clutch situation, and know what they had there. It's not easy to have the nads to put Bledsoe on the ground, but the discipline of the business end combined with the smarts of the coaching/personnel end to make it the obvious move.
There's a phrase, "you make your own luck." The better-run teams do that repeatedly, while the less well-run teams tend to "reach", wishing they could make that kind of move.
The Pats went through the depletions that a multiple super bowl winner is heir to. Every free agent is overvalued because of his ring. What did we do? Let them walk... and still competed with what we had.
Then when the stars aligned... well, we all watched what happened this summer.
Okay, enough crowing. I think this illustrates that there are winning approaches to football that overshadow the talent one is able to field any given year. This busts the whole idea of parity, to a certain extent.
But these other aspects of football are now in the spotlight, since the talent aspect does not simply pool in one or two dominant teams anymore. Still, bear in mind -- these other inequalities also existed in previous eras. It is just that now, they become the remaining variables (to an extent), as player talent approaches the status of a constant.
So is Parity a failure? I know a Giants fan who thinks they're still going to the Super Bowl, even though they're 1-2. I don't think the Saints have given up, nor have their fans. With a 16-game season, I've seen teams "out of it" by mid season who are right there at game 17 every year. I bet you could collect stats on this, but I'll just lean on the anecdotal for now.
People turn on the TV and root for their team, not out of dumb loyalty, but because their team could win it all. I remember being a Pats fan in the down years... sometimes we were in a bleak quarterbackless desert, and I just thought during game 1, "we'll get 'em next year... or maybe not."
I don't think there's as much of that now. There are too many "rags to riches" stories. We're all undefeated, as the NFL commercials say at the start of every season... and we all actually buy into that.
PFnV