Normally, in cases like this, the law prohibits businesses from offering gambling services. In that case, no Americans would have broken any law.

However, a quick google search strongly implies that sports betting is in fact legal in Maryland. http://www.legalgambling.net/is-sports-betting-legal-in/mary...

Something is amiss.

Edit: While the Rosenstein quote erroneously states that "Sports betting is illegal in Maryland", it seems more likely that this was actually a breach of the 1961 Federal Wire Act, which banned sports betting over the wire. If Bodog allowed bets to cross state lines, then they're involved in interstate commerce, so the Wire Act applies.