Sources are publications, so things are proven by what established media says. Difficulty arises when publications are more likely to repeat a narrative than originate it (herd safety). As such the problem becomes: "Freedom of the press is guaranteed only to those who own one" - only now echoed in an supposedly neutral "pedia".

Notability is the same problem: something is notable if there is published media about it, otherwise not so. My perception is relevance and truth are being outsourced to 3rd parties based on whether or not you blog post has corporate registration.