I think as far as Governments are concerned, a Digital Currency is anything digital that people are prepared to swap for cash. If people were prepared to swap monopoly money for real cash, then governments everywhere would try to regulate it, even though it's not digital.
What about mp3 or movie files, or software programs then? Seems kind of unlogical that those would be considered digitial money.
There is a dev on here trying to sell BEEPs as a new form of crypto. Apparently each one sounds like a different farting noise, and he expects people to use them as a currency, though I don't think they are on an exchange yet.