I seem to remember several years ago, when the overseas account declaration thing first started hotting up, there was a court case about it, Mr Tel-un-tel versus the fisc, and that was the ruling. It was widely reported at the time and AFAIK nothing has changed. I imagine the case and the ruling are still google-able.
I don't see why currency exchange accounts need reporting, they are not new income are they, they are just moving your own money around and that money already has a trail through your bank or whatever. But with paypal accounts you can receive income via paypal, keep it in your account and pay it out again, it never touches any other financial institution and it wouldn't be recorded anywhere else.