That's because billionaire means nothing. e.g. Jordan Belfort was almost a billionaire, but still went to jail like small fry.The untouchable ones are oligarchs, that is what people are implying and it is much scarier to have a 6-year-old messing around as one.
Madoff made the mistake of stealing from people more powerful than him. Billionaires always steal from poor people, and thus incur no wrath from people who could punish them.