Yeah, and also; Amazon knew (or, at least, Bezos says he knew) from Day 1 that books were only the beginning. They started with books because they're an extremely broad category (hard to stock one Barns & Noble full of every book), easy to ship, and they have a practically unlimited shelf life (versus clothes/technology, which experiences seasonal trends, or even food; all of which Amazon now does).

Big difference between "we think this is The Business, ope its not lets pivot" and "we think this is a good place to Start the Business and grow out of".