My answer is no. I like biographical novels, but I also like historical novels about fictional people. I can always pick up a nonfiction book to learn more about a specific historical person or event.
However, historical nonfiction is often very dry and academic. (One of the most boring books I've ever read was a biography of Mozart; don't ask me how the author managed to make him so dull.) Maybe that's why some readers turn to fiction to learn about history. Maybe there's a need for more entertaining — not dumbed down — historical nonfiction. Just a thought.