It has nothing to do with Bitcoin. He was exchanging SOMETHING for USD. CampBX by all reports is properly licensed. Their Dwolla is working just fine.
Of course it has to do with Bitcoins.
Amazon accepts USD for DVD. They also pay USD for DVDs. Is amazon (and every retail business in the world) a MSB? I mean commerce by very definition is the acceptance of money for goods & services.
However FinCEN provided guidance in March, 2013 indicating that virtual currencies* are subject to MSB regulation:
http://fincen.gov/statutes_regs/guidance/html/FIN-2013-G001.htmlThus it isn't that MtGox exchange "something" for real currency but that they exchanged "something which is regulated by FinCEN" for real currency.
Prior to March, 2013 there was no real reason for MtGox to register, post March, 2013 I am not sure how/why (as the worlds largest Bitcoin exchange) they thought they would remain under the radar.
* Only entities which buy/sell/trade/exchange virtual currencies for real currencies fall under MSB regulation. FinCEN does indicate that buying or selling goods & services for virtual currency is not a MSB.