Can Someone Please Explain?

An important gap filled: I have finally seen Days of Heaven (and understand now why Bob Mondello called it Days of Wheat.) Yes, it's stunning. But the accents. Oy! Were they lying when they said they were from Chicago? (If so, you'd think there would be some kind of clue.) Are we to believe that, in the first decades of the 20th century, the windy city was inhabited by New Yorkers? Or that in 1978, America couldn't tell the difference?