What's stopping or making it difficult for MtGox to *create* those cheques and mail them out?
I really do not know what you're talking about. How to create a cheque in Japan which is accepted by a Bank in your home country? I would guess that this is impossible. I've never seen anything like that. This works within the European Union. But the banks take astronomical fees. And a cheque from Japan? Not possible. No Bank will accept this. You have to travel to Japan to redeem it.
It's much easier to open a bank account in Japan. Why are not doing that? You can get your money from Gox in ¥ if you need it so urgent. Dollar not possible, thanks to the FINCEN.
Cheques are dead. Nobody uses cheques these days.
Actually in the UK they are still widely used. In fact they are probably the main way of making payment between individuals and/or small businesses that don't have card facilities (of which there are many). I would certainly expect my bank to accept a cheque drawn on a Japanese bank, though there might be some fees involved. But it may be different elsewhere.