[detourdog]

I think the original comment might be getting at the cultural differences between the US and Japan.

It is plausible to me that the group that owns the most Japanese Yen get to set the rate. That group can decide to tread water or start to charging outsiders for use of the capital.

Warning the above is wild speculation from a stranger on the internet.

[pjc50]

All central banks get to set a "floor" rate by virtue of being a central bank. Commercial banks then charge a "vig" on top of that.