If you need any more proof that the game has shifted away from one that is focused on the running game featuring RBs, interior OL-men, and MLBs, you need only look at the FA signing waves this off season. Rather than focusing on the inside power, the league is all about passing and speed on offense and speedy pass rushers and CBs on defense. The game has shifted to the edge - outside WRs, edge pass rushers, CBs and speedy outside LBs. Nothing new here, everyone knows this and I have been posting about this here for several years. For example, the desirable WRs all signed big deals and edge rushers and CBs also got rich. Conversely, Peyton Hillis, who is perhaps the prototypical RB of a previous generation, and whom everyone thought was going to be a much sought after RB, signed as a backup RB on the Chiefs. Meanwhile Megatron, DeSean Jackson, Vincent Jackson and a variety of other top WRs also signed for big money. Giants saw this coming and are ahead of the curve here - it's why all of the LBs they signed last year were speed guys, not Dick Butkus / Sam Huff types.
But - what about the second layer of WRs, Giants Super Bowl hero Manningham - why hasn't he signed a big contract and why hasn't he even attracted a little bit of interest. There could be a few reasons to explain this phenomenon. First, and most obvious is that there are a lot of players available, a lot of talented WRs and Mario is maybe 8th or 10th on the list. Capitalism at work: with a glut of supply, prices / salaries weaken. Teams may feel that if they sit tight, they can get Mario at a bargain price and while he's very good, he's not great and not in the same league as the elite WRs in the game today.
Nice simple explanation, but I think there's more than that at work here. It is obvious from these signings that WR is the new glamor position in the NFL. A few years ago it was RB, now it is WR. From a financial perspective, it may be even more desirable than the QB, since there are only 32 QBs in the league, while at WR, every team is looking for 3 starter type WRs, meaning that there are 96 such desirable position to be competed for. Therefore - if you were a father who had a son with big athletic talent and you wanted to groove him and train him for a professional football career - your best shot is to give him some Nike catching gloves, a Juggs machine for the backyard to throw passes to him and sing him the famous western ballad: "mama don't let your babies grow up to be running backs" (with apologies to Willie Nelson). WR is the position of the next decade of NFL football. There are more opportunities, fewer injuries, therefore a longer career and more earnings potential. Nice theory if you buy into it and here's what it means. A good percentage of the best athletes really are going to become WRs, which means that every year there are going to be more and more speedy, dangerous, game breaking WRs coming out of college. If you have a stud like Calvin Megatron Johnson on your team - pay him, lock him up and be happy. However, if you have a very-good-but-not-great WR like Manningham available, don't empty the cash drawer or mortgage the farm to pay him. Instead, be confident that there's going to be some speedy, big, talented WR coming out of college every year that can fill in very capably and give the offense juice. On the Giants, I love Nicks and would make a commitment to him. Cruz is in second place and I would pay him some money, but not go crazy with him. Jernigan will get a shot this year and maybe he will turn out to be a good slot player also to replace Cruz if he busts the salary cap. And Manningham - he has good speed and is a good compliment to Nicks / Cruz, but there will be somebody coming out of college that can fill his role for 1/2 or maybe even less of what he probably wants in salary.
Giants resigned Hixon, they have Barden on the team as well as Jernigan. If I read between the lines correctly, the coaches like the progress they have seen from Jernigan in practices during the year. He got into a few games during the playoffs, though he didn't do anything at all. Further, Coughlin several times mentioned him as a player to watch next year, someone who might get a chance. They need some speed at that 3rd WR position, although maybe Bennet at TE provides that other threat that can't be covered with LB.
So I think all teams are looking at wave after wave of good WRs coming out of college and are only signing the premium veteran WRs to FA contracts.