But, they have to operate within legal boundaries, as Food Lion Incorporated v. Capital Cities/abc Inc 194 F. 3d 505, demonstrates. These investigative stories don't come without some legal peril for the journalists doing them. Criminal prosecutions are probably rare, if only because of mens rea.
"WB trots off and steals the relevant data, provides it to journalist who publishes it. Sounds like conspiracy and accessory before and after the fact to me, and except for the national security connection exactly what Wikileaks is accused of."
This really isn't my area of practice, but I wouldn't be at all surprised to learn that there may have been prosecutions (or at least indictments) in just this kind of case. I'd guess though most prosecutors would exercise more cautious discretion in bringing such a case.
It is the national security element that makes this so much different. Quite literally, the stakes are so much higher.
I should have added, that if it turns out that Assange was just sitting in his office, and these materials plopped on his desk (or his computer inbox), then he has virtually no criminal exposure here. New York Times Co. v. United States absolutely guarantees this.