You missed a key part of the story where the undercover agent told the bitcoin seller that he was going to use the bitcoins to purchase stolen credit card information.
That is the least important part of this case.
This may be the least important part of the story to
you, but it is an absolutely critical part of the money laundering case. There is no way they would have indicted these guys for money laundering without that. Even if they had, the prosecutor would drop the charge to avoid the embarrassment of an acquittal or, worse, a dismissal.
However, I agree that this is not particularly relevant to the charge of running an unlicensed money transfer business. One thing that is unclear from these indictments is whether the sting was intended to uncover money laundering or just unlicensed money transfer.
It will be interesting to see whether these cases go to trial. It seems plausible to me that they will want to use these cases, in which a conviction will be relatively straightforward, to establish a precedent. If they truly just wanted to nab these two guys, then I would expect expect the defendants to plead out. The prosecutor might not offer them a reasonable plea deal if they want the precedent for future, murkier situations, such as cases connected to Silk Road.