http://en.wikipedia.org/wiki/Daniel_Ellsberg
And also I'd be wary of setting MLK as a golden standard- I'd say his image is very whitewashed, and very much used in ways that he himself would have opposed (ie: all the kids who are obliquely taught that he "fixed" racism)
Most British whistleblowers wrong-footed themselves with 9/11 or decided they were Jesus, they didn't need the media to make fools of them. I don't think that what's his name again? will make this mistake. However, there is a 'now what?' aspect to the story, there is no uprising from the masses, marches on Washington or anything troubling for the authorities.
In some ways Snowden has helped formalise the spying arrangements, it is now just a fact of life like having CCTV everywhere. The social contract has just been clarified.
Also, Snowden did one act, albeit a lot of planning and hard work went into it. He is not recognised as a writer or a public speaker (yet). His babysitting arrangements mean he cannot flourish that way to easily.