Imagine what would happen if the US Govt decided to hodl DPR Seized Coins as cash asset, instead of auctioning them off.. They never auction money/cash/fiat that's seized. Since the judge declared bitcoins as money, and if the FBI holds them based on that, it would give Bitcoin so much credibility having the a federal agency holding bitcoin on it's balance sheet.
AFAIK, cash is simply handed over to the Treasury, and they are supposed to use it for the People's benefit. The Treasury knows how to handle foreign currencies, so those are sent to them too. Other stuff (including bitcoin) must be converted, by auction, into dollars that can be sent to the Treasury.
The DPR judge did not rule that "bitcoin is money", only that it counts as money for the purposes of the trial, because it is what DPR took as his fees from SilkRoad's illegal businesses. If he had taken his fees in diamonds, it would have been seized and auctioned the same way.
Courts and police understand that "money laundering" can be done with any valuable stuff, such as gold, diamonds, real estate, boats.
I suppose that "money transmitting business" would include also a service that accepts gold from one person here and delivers it to another person way over there.