Not quite. Pittsburgh, Dallas, GB to name a few successful franchises have always had loyal fans as well through thick and thin. The only team that comes close to the Pats in the bandwagon fans regard is Seattle.
My ex and three kids live in Nashua, NH and her huge extended family are all from Boston and all Pats fans. Her father agrees with me 100% about how unfaithful Pats fans are. As someone else stated, its always been a baseball/hockey area first.