Wealth is not as great a motivator as people think and motivation and ambition exist in a broad spectrum. Most people want more money, yes, and will work harder to get it. But in order to "excel" (like Gates did) requires a different kind of ambition. It's a very complex issue, especially because we tend to mix professional success with wealth and because growing in a wealthy family grant you certain expectations, education and networks of friends that steer you toward certain goals.