That isn't the same thing, and your anecdotes don't really mean anything; the parent's anecdotes act as a counterexample, which is all that is necessary to prove that ID isn't necessary, even if it's generally or often used.

AT&T is requiring you to show ID as a security measure, not because the US gov't requires it. You're talking about them using your ID for authentication, to protect you from someone impersonating you to make unwanted changes to your account. This does not preclude you from being able to walk into an AT&T (or T-Mobile) store and get an activated SIM card with cash and without showing ID.

Ditto for the hotel security guard check. If they had required your ID at check-in for any purpose other than authenticating you against their reservation record, then that would be a problem. If you could walk into the hotel without a reservation and pay for a room with cash without flashing ID, then the parent's point stands. (And even if you couldn't, this may just be a particular hotel's policy, which is fine. The point being made is that the government is not requiring this. There are plenty of hotels in the US that are perfectly happy with anonymous money.)

As for flights, there's definitely more government involved with ID'ing you, but you can absolutely fly without ID. You just need to go through extra security screening, which is a pain, but works just fine.

My experience in China is over a decade old, so I won't comment on that.