The guidance doesn't make "anyone" an exchanger because there is an explicit exemption for "users" purchasing goods and services who are not in the business of buying and selling currency, so I disagree on that point as well.
You miss the point. Anyone who exchanges virtual currency for real currency is an exchanger is one way to interpret the guidance. So say MtGox becomes a MSB. Great now every on of MtGox clients would need to also. They all are "exchanging virtual currency for real currency". The guidance provides no exclusion that those exchanging with regulated exchangers are themselves exempt. This would make anyone who ever has or ever will exchange real currency need to register as an MSB. It seems implausible that is FinCEN intent however by the letter of the guidance it is what is stated.
The guidance is unclear, it is just my opinion but only clarity from FinCEN will resolve that lack of clarity for me. That is the point of an administrative ruling. It certainly is possible that the AR will result in more clear guidance one that advises that the example in section c is not binding any such trade of BTC for USD constitutes an "exchanger". The good news is it would remove ambiguity from the definition and force FinCEN to clean up their guidance. Is it FinCEN intent that anyone who ever buys or sells Bitcoins for real currency needs to register as a MSB? I really doubt it but if so the AR will require them to state so in black and white.