To me, corn is a traditional Thanksgiving vegetable. There's the tradition that the Native Americans taught the Pilgrims how to plant corn, and without the corn, they might have starved those first few years. I think in one of the Little House on the Prairie books, Laura talks about always having three corn kernels at her place on Thanksgiving. Something about at times, that was all the Pilgrims had to eat. (I could have the author completely wrong, though.)
My dad always had a garden, and Mom would put up some of the vegetables just for Thanksgiving. We ate most of them as they got ripe, but we always had green beans and carrots from the garden for Thanksgiving, and frozen corn.