I wish this were true, but it's not.
Every offseason the Cowboys, and I'm sure a bunch of other teams, take base salaries of players and turn them into gigantic "signing bonuses" so their supposed cap-hit is only a fraction of what it should be. It's how the Cowboys were able to resign guys like Ratliff, Ware, and Austin.
I'm sure the Giants will do the same thing, especially with Eli's contract. They'll give him at least 7 or 8 in bonus and turn that 13 mil cap hit into something much smaller, and they can do that for a few other players as well.
It's bullshyt that you can manipulate the salary cap like that, but all teams do it, and I'm sure the Giants will find a way to soften the burden of big contracts. I think they'll let Nicks walk, to be honest. Giants should have no problem locking up Cruz, since he gets 10+ targets a game, and then pursing an Alshon Jeffrey type of WR in the draft that can be groomed to run the over-the-top Z routes that Nicks does (when he's not hurt

)