This is exactly right. Daniel Ellsberg broke the law by photocopying and smuggling out classified documents about Vietnam War progress (or lack thereof) from the RAND corporation, where he was an a Ph.D military analyst. He provided those documents to the reporters from New York Times and Washington Post. The Nixon Administration filed an emergency injunction with the Supreme Court to suppress immanent publication by the New York Times. But the Supreme Court refused on the grounds doing so would imperil the first amendment by imposing court mandated prior restraint. See: New York Times v United States.
Now that does not mean Ellsberg could not have been prosecuted under the Espionage Act of 1919. He absolutely broke the law and admitted as such. He was an employee with a high security clearance entrusted to prevent the release of those documents. Not steal and release them. The justice department ultimately refused to prosecute. But as we've seen with the Bush and Obama Administrations, Espionage Act investigations and prosecutions are popular these days.
Just how the US Government plans to prosecute Assange under the Espionage Act is unclear. He's a non-citizen who never signed a US security clearance nor took an oath to protect classified materials. Furthermore, Wikileaks is arguably a journalistic endeavor. The government makes no distinction between official journalists and citizen journalists for first amendment protections. If the New York Times can do it, so can Julian Assange. And if they argue he's not a citizen and therefore not protected under the first amendment, how then can they argue as a non citizen he's bound by the US Espionage Act?
Perhaps a real lawyer can chime up here. I just took a grad media law class. But it sure seems like tortured logic to me.