Your mistake here is missing the idea of "due diligence". Many laws (in the US especially) revolve around this concept. The basic gist is, has the concerned pa

Your mistake here is missing the idea of "due diligence". Many laws (in the US especially) revolve around this concept. The basic gist is, has the concerned party taken "reasonable" (vague on purpose to adapt to evolving circumstance) action to comply with the law. In the instance of serving alcohol, everyone carries an id and carding is judged to be the level of "reasonable" action; in contrast, on the internet where access to identifying info is much sparser, user verification makes the cut. It's not a contract being form, it's the company in question performing the minimum viable verification to protect themselves from liability.