First, it may not be specifically protected in the Australian constitution, but they definitely have free speech. Otherwise the government would be free to tell Mumbrella and other news outlets what they can publish, like the CCP can and do with media outlets based in China.
Second, I'm not sure exactly how defamation laws work in the US, but people can most definitely sue if they believe they're misrepresented. The 2nd amendment protections for free speech constrain Congress, not the courts.