I'm having a tough time to determine which way I stand on this.
Part of me thinks that its fair. It sounds like the Redskins, Cowboys, Saints, and Raiders rather egregiously frontloaded the base salaries of players to hit during the uncapped year, thus creating all this cap space for this year. This coming after the league warned teams about this very practice ahead of time. Essentially defying league mandate. In a way, its salary cap circumvention which has been a problem in the past for the league.
On the other hand the league, itself, created an uncapped year and these four teams took advantage of it by paying large base salaries in a year where it wouldn't matter. Good business, in a sense. Also, it sounds like a warning was issued, not an actual rule was set. Then you have to wonder if the 28 teams that did sign players to contracts in the uncapped year were guilty of some sort of collusion to keep the base salaries down when they could've clearly paid some more without salary cap ramifications. I'm sure the NFLPA won't be thrilled by that.
Right now, though, I have to think that if the league issued multiple warnings about this, why the heck would you go out and do that exact thing then unless you feel certain that the mandate violated some sort of law and wouldn't hold up in court? 28 teams seemed to abide by it while 4 did not.