In my mind, what distinguishes the Snowden case from the Assange/Manning cases is the distinction between whistleblowing [1] and a fishing expedition [2]:
> A fishing expedition is an informal, pejorative term for a non-specific search for information, especially incriminating information. It is most frequently organized by policing authorities.
The question is whether it is lawful for any group to mine a corpus of private documents searching for a crime or misdeed. Individuals or small activist organizations now have this ability and it is not exactly the same as a whistleblower leaking documents associated with a known crime.