I think this is a question of what your definition of "a lot" is. If you use percentage - for example, 1% of parents, of maybe even less - 0.01%, 0.01%*7.7 billion = about a million people.

Does percentage make more sense here or absolute number? It depends on your context. I would say in this argument, it seems more certain that Von Neumann's success, which is always a function of both nature and nurture, can probably be attributed more to nature. Or, perhaps most likely, it's a rare event of talent meets incredible luck.