From other comments: Vanguard's 500 index manages ~500 billion (dmoy), Gates is worth ~100 billion (kevindqc). Even so, Vanguard can't just increase their fund by 20% like that.
Right you're sorta missing the point though. Vanguard outside of the s&p 500 has another 3.5 trillion or something. They could absorb bill gates net worth.