Cranky Yankee - wild grapes are, were, and have been much more widespread then just Martha's Vineyard and Rhode Island.

The 'Concord' grape (for example) is a sport of wild grapes found near concord Massachuseets and propagated since.    Wild grapes also grow (and have grown since before colonial times) throughout most of NY state - The southern US has their own species of grape that doesn't grow in the northern states.