I think it's different because of the message it sends. Using bitcoin to do generic illegal things is an 'offense' to anyone that wants to stop illegal things. But there's already lots of targets to aim for if somebody wants to enforce the law, the method of payment is kindof a small deal. However, in this case using bitcoin is an offense to the other party in the war -- the US. I think the US has a more obvious target, and is more capable to do something about the "problem" than general law-loving-folk are about illegal activity. At the very least, I'd think it breaks the embargo? And the US really has (historically) cared about that.