This discussion has been had lord only knows how many times. At this point, the only people who don't get it are the people who are purposefully not getting it.
It's not just a Felger/Mazz thing. BB's pointed it out. Media and GMs all over the league have pointed it out. The actions we're seeing this offseason point it out. The teams don't even pretend it's not, as can be seen by the fact that they acknowledge the difference between cap numbers and actual cash paid in the CBA. The cap is almost entirely just an accounting gimmick.
And I'm not saying that to deride it. In a game without contract guarantees, and with large in season turnover due to injuries, there has to be a way to account for all the needed moves. I just think that we all should be long past the time where we pretended that the cap, as a general rule, offers any real impediment to player signings beyond what the owner wants it to.