Reason for the Packers' cap space

In peering at the salary cap data released by the NFLPA, there are some teams who still have more than $10 million in space in spite of already going on something of a spending spree (Cincy, Cleveland, Philadelphia). Teams like the Jaguars and Buccaneers have a lot of cap space, but this makes sense, since they haven't signed any big contracts. One team whose cap space may be a little puzzling is the Green Bay Packers. But there's a reason why they've given themselves that cushion.