If you have money, you can generally send it somewhere else. If you don't...
They can. Withdrawal of JPY to Japanese bank accounts work fine and arrive next day. JPY has sailed up as the third most traded currency at MtGox now, and the price difference between MtGox and Bitstamp is slowly decreasing. Below 10% for the first time in days now.
Do you know for a fact that withdrawal to a Japanese account is doable? The yen rate for BTC at Gox is as high as the dollar rate which would suggest that it is no more possible to withdraw yen than dollars.