Wonder if it's something like this... Patriots want to keep McCourty and want to pay fair market value, but don't necessarily want to do so this year because of the cap situation. So, they franchise Gostkowski whose $4.5m number is lower and equal to what they would have to pay to extend him anyway, shelve that negotiation, and then continue working hard with Revis while continuing to let McCourty know they do want to keep him. Then, they extend Revis and clear up some cap room, and at that point have a good idea how much money they really are comfortable spending right now. They let McCourty hit the open market and test the offers he gets, keeping lines open.
It's probably true that the Patriots will be outbid by another team, but that doesn't necessarily mean McCourty will go there. Would YOU want to go play for the Indianapolis Crybabies for say, $11m per vs. $9m per from NE? I think BB has some faith that he may not have the biggest checkbook, but he is the one who raised Devin in the NFL and it will be hard for him to leave home unless the deal is really blockbuster, and what can you do then? (for example, Denver blowing their load on Talib last year)