Bitcoin is in many main languages but not Japanese. Why would the guy who created it not make it in his own language? Don't you find it suspicious MtGox is in Japan?
Also the project really isn't a success. A lot of progress still has to be made. Security is still an issue along with sites still growing. Anyone ever even talk to him? I'm not saying he isn't real I'm just putting this out there.
Satoshi do exists as he is the one who created bitcoin but we do not know who was he exactly.
Secondly, there is no issue with bitcoin security therefore people have trust in it and they invest their money in bitcoins. No matter how many centralized sites are created, it's our responsibility to keep our bitcoins in decentralized wallets.