Forbes has released their list of the 40 richest people in Japan, and a familiar name is at the top: Nintendo's former president (and current guy who receives a lot of money), Hiroshi Yamauchi. Yamauchi still owns a bunch of stock in Nintendo (the company founded by his great grandfather), and also probably retains the right to Satoru Iwata's lunch money whenever he sees Iwata in the hallway.
You don't even need to make any sly references to the rumors of Yakuza connections to explain Yamauchi's remarkable $7.8 billion worth. The sales of the Wii and (especially) the DS more than adequately explain how Yamauchi could have become so wealthy. This seems like a pretty good indicator of Nintendo's success.