I think many speculate that Satoshi burned up the private keys for lots of his Bitcoins.
It's a profound realization that if he ever moved any of his bitcoins or made an attempt to sell even 0.00000001 BTC (one satoshi!) Bitcoin's price would likely plummet.
For a person so rich in such a transparent currency, anonymity is the only way out. Then there are those who suggest Satoshi is an alien 