There are many billionaires such as Warren Buffet, who doesn't own any coins at all. What about that? There are some billionaires who have invested in Bitcoin, such as Winklevii and Michael Novogratz. There are also a few such as Buffet, who have refused to invest in Bitcoins. And then there is the third category comprised of people such as Musk, who have collected a few mBTC, just for fun.