That's only true in journalism. Just because we link to news stories primarily doesn't mean this site has a journalistic flavor or should follow those conventions.
Attributing words to someone is something one should be cautious about, regardless of the context. It isn't a peculiarity of journalism.
I was responding to the idea that such a convention about quotation marks doesn't exist. It absolutely does. Journalism is the most familiar example, but academic writing, non-fiction books, and other contexts are held to the same standard.
