Whistleblowers can publish this material themselves. However, once you publish the material, you also need to make sure that mainstream news sources pick up on

Whistleblowers can publish this material themselves. However, once you publish the material, you also need to make sure that mainstream news sources pick up on it and report it, otherwise you are just some guy with a blogpost somewhere. Wikileaks is now a "brand name", if you will, and leaking through them makes sure that, unless you yourself decide to confess like Manning supposedly did, you both remain secure and yet are noticed.