It's obvious it works. Is there flexibility? Yes, there is room for some. But part of the reason is because they are so responsible in the first place. If they made exceptions for every single situation, they simply could not afford to do more. Welker's franchise tag last year when they valued him around $5M is an example of this. Or maybe Wes was worth more last year because Amendola wasn't available. The point is that the Pats always have room to make moves, while dozens of teams are cutting guys they don't want to but have no choice about over the last few months.
Also, I don't know if we invented it or not, but if you look around the landscape, you'll notice certain teams follow similar principles. The Ravens could have matched some of the offers on starters signed elsewhere, and I'm really surprised they didn't match Ellerbe's deal. Everyone is writing them off but they may have a chance to come back with an upgraded and healthier defense than last season. San Fran has a bloated defensive payroll but they are big on signing/keeping their own FAs and complementing them from the outside. Their fiscal discipline allowed them to absorb Boldin's contract when the Ravens could not. Green Bay has also lost players rather than pay them inflated salaries, the most recent example being Jennings, yet they've found a way to consistently compete. Ted Thompson sets an even harder line than we do it seems. These are some pretty good franchises to be associated with.
Then you have the Jerry Jones and Daniel Snyders, the Raiders under Al Davis, the teams that constantly had to have that one guy and would pay any price to do so. That's how you end up franchising the same over-rated DE twice or signing blockbuster failures like Haynesworth or giving $4M a year to a punter.
I hate to throw Tampa Bay in here but that Dashon Goldson signing was downright irresponsible. 5 years, $41M with $22M guaranteed in a flooded safety market where LaRon Landry is getting $6M a season (what???), Ed Reed is getting $5M per, Adrian Wilson less than $2M each year, and Kerry Rhodes is still a FA. Jackson was a great signing last year, but Nicks sat out half the season after his big deal and Wright has been a terrible deal in multiple ways. With a flat cap over the next few seasons and Freeman's $8M contract expiring this season and potentially having to pay double-digits to their QB, they look to be heading straight for salary cap hell soon.