Thanks for that graphic - that is an impressive difference.
Though it can definitely be milder on the water under normal circumstances, but I think what's interesting in some areas this winter was, ok, once the water freezes, what are you left with? Only topography to help you. I'm usually bumped up a little bit by the upper Bay. Not this year, it was a big white sheet of ice during the coldest nights. (but is quickly thawing now)
So if the water around the Vineyard froze, and I don't know if they did or not, could there have been a night where the airport was actually warmer, because cold air could drain? Maybe, maybe not, I'm guessing its elevation is only 50 ft. at most. (ahh, google says 67' I was close)