It really doesn't matter who Satoshi Nakamoto is but, of course, it's still interesting to speculate. Contrary to many others I don't think that S. N. is a pseudonym for a team. IMO S. N. is (or was) a single person. That he never touched his fortune in years strongly indicates that there is no team involved but rather a single player. There are many possible reasons that the coins were never touched again. The explanation could be even something simple like a broken harddisk, a lost USB-Stick or a forgotten password. But there is also the possibility that S.N. died without leaving any instructions to his heirs.