I think it's more likely to be arbitrage traders making alot of money on this opportunity.
Arbitrage with what?
43800 JPY is 438 USD which is close to what MtgoxUSD is trading.
They can pull JPY directly out of the bank in Japan from MTGox. IE they're the only ones who have liquidity with MTGox.
So for them the higher gox proce and quick access to funds makes arbing by buying at lower priced exchanges simple easy money