"In the United States, the federal government legally contends that no such protection exists for journalists."
There are well documented cases (and even a movie based on true events) of journalists having to go to prison because they wouldn't reveal sources.
e.g. Found this on Google searching "reporter source prison": http://www.theblaze.com/stories/2013/04/08/as-fox-news-repor...
For information that is best delivered anonymously, this sounds like one of many tools to get your message out there.
[1] http://www.npr.org/2013/05/14/183810320/justice-department-s...
Why do you think Wikileaks was invented?
What does that even mean in a time when the US government can pressure reporters into giving them the information anyway, or simply spy on them (see AP spying case).