The two are quite distinct from one another. Either information is of a public or a personal nature. Anything that falls in a grey area ought to then be considered public since clearly then it becomes suspicous. The two ought never to mix.
In a perfect world, there would be a clear division between public and personal info, however, we do not live in a perfect world... The Minister of Foreign Affairs for the UK is a matter of public record, but because we know his name is Joe Smith and we can source info on Joe, we have also ventured into the realm of private info.
Let's not confuse theft with treason. Treason does have a very technical definition. Assange was not working for any foreign government, and seeing he's not even a US citizen, he can't be considered a traitor to the US. By definition you can commit treason only against your own.
Assange and Manning have done both. One need not be in the direct employ of gvt in order to pass along sensitive info that will have an impact on a nation.
Further, the USA is not the only nation with 'treason' as a charge. Assange is (presumably) a UK citizen and if he released any cables from the UK diplomatic corps, he would be charged under UK law... On that note, the outside nations of which Assange is not a citizen, also have serious charges against spying.
I'm guessing that Assange would be extremely careful in terms of which nations that he is prepared to enter.
As for Manning, the charge of treason is more debatable since he was a US citizen, but again was not working for any foreign government or "enemy" as such.
There is no debate on this. Manning will be convicted of some degree of treason