here's an example of nun's point: a forex company, like HIFX or Moneycorp (regulated by the FSA). You contract with them to buy, eg, xxx GBP for xxx USD, now or in the future. Is that a 'financial institution'? If I try to answer the question I think: on the one hand, it's just a contract but on the other hand, if the spirit of FBAR is to follow the money, then maybe that's the kind of thing FBAR is meant to include. It's not transparent.
As to the professionals, all they are trying to do - as they must for their clients - is answer a question in the absence of clear law: what analysis would win if challenged in court (which is the ultimate determiner). For the courts, the effect of the analysis, interpretation, decision, etc on the ordinary TP is hardly a consideration.