Update. I just read up a bit on their migration habits and found that some Robin's will indeed overwinter in the Northern Climes, and if they do they switch to a fruit diet. They will also "flock" together and are less territorial.
I personally have never seen a Robin "overwinter" up here. I'm going to have to that house again and see if he's got something special growing that is keeping a small flock of Robins in my town!!