Poe, for instance, basically invented the detective story. Now that may seem trivial, but how much money has been spent on such in the US since he died? How many people were employed writing, printing, and selling detective stories? How many people were influenced by Poe, and in turn wrote their own books and stories that employed all those same people?
It isn't so easy to write people like that off, really. Harriet Beecher Stowe was just a writer, too. Hell, for that matter, Jefferson wasn't much more than a writer.