Scoping to a reasonable level, publishers' primary job is to review and filter information for quality, safety, and fitness for mass consumption. Assange and WikiLeaks explicitly do not do that. At best, they are a distributor.
The law generally views the publisher as responsible for unlawful (defamatory, copyright infringing, etc.) content without evidence of specific knowledge, whereas distributors are generally liable only when they have specific knowledge of the facts that make the content unlawful. This, in effect, makes publishers responsible for reviewing/filtering content, because if they fail to do so, they will be held responsible.
That's the whole source of significanxe of, e.g., the section 230 protection against hosts or other users of online services meeting certain descriptions being treated as the publisher of other-user submitted content.