Plenty of ways to add to the cap. The Dolphins can essentially be up to $14M under the cap if they wanted to. There's also the provisions allowing you to be over the cap by 3 contracts being sorted accordingly. Don't have the exact wording of this stipulation in front of me right now at the moment, but I know it can be done as a couple other teams are using these methods with the new cap rules. These provisions add millions to your cap.
The bottom line is If the Dolphins played their cards right they could be close to $15M under the cap.
To add to that, Cut guys like Sapp, Culver, etc etc as well as working on a Soliai extension, and maybe reworking Jake's contract to give him more money up front (this is why players rework contracts as they get big money upfront) easily accomplishes PLENTY of cap room to sign 3, or even 4 good players.
So that's no excuse. This team could easily have added guys like Zach Miller, Carl Nicks, another decent to good WR/RB, and maybe another good defensive player if they really wanted to.
The GM of the Jets is great with the cap and it's why they can have room for really good players every year. In one day last week, he restructured 4 big contracts on his team to free up about $7 or 8M in capspace in a day. And hell, it looks like they're about to resign Cromartie now too. We need pro-active people like this in our FO so we can go for the jugular too.
If the Jets didn't have a fast seam-busting TE like Keller, but instead had a slow sloth like Fasano, you know that the Jets would go after Zach Miller hard and find a way to get him under the cap. That's why they're in the AFC Championship every year and on the cusp while the Dolphins are out fishing when the postseason rolls around.
I hate the damn Jets but you have to admire how their front office gets it done and how they're so pro-active. I guarantee you if we had Revis on one side at corner for our defense, that Ireland and company would never consider or contemplate trying to get Nnamdi. But not the Jets, they still try to get the best of the best. They don't catch them every time, but damned if they don't try and go after the best as much as and as often as they can.