but isn't it just as obvious that plenty of people with that kind of riches aren't in business, government, or the power-focused professions?

Sure, but often they don't accomplish as much. People with high intelligence and low drive. And they aren't as concentrated. Generally, the only way you can really get smart people together is if there's an economic reason. Otherwise they're distributed rather evenly throughout the population. (I would say universities count as economic.)