That article sounds kind of old. How many years ago did they stop asking whether one's bag has been left unattended and whether one has accepted gifts/items from a stranger?

So it's been established that there is no directive from the government to airlines to deny boarding to a customer solely on the basis that he/she can not or will not show a government-issued photo ID. Does that mean that airlines are not allowed to deny boarding to someone solely on that basis, or is it simply left up to the discretion of the individual airlines?