I think this is legally required in the US, if you book directly with the airline. This is a solid reason to never book through the flight aggregators.
It's also required in the EU. It happened to me with British Airways
AmEx provides me this benefit when I book through them.
Expedia provides the same cancellation period as well. It saved my butt once last fall when I clicked on the wrong month in the calendar. Plus I have used it for other flight cancellations with them.
They legally have to. Always amazes me to see airlines boast of their 24 hour refund policy that they don't actually have any choice over.
I mean, clearly a lot of people don’t know it’s the law, so it doesn’t hurt advertising it as a perk. Especially if the other guys don’t advertise it.
This was also the strategy of ep 1 of mad men — lucky strike’s “it’s toasted” slogan — if you say it first, then despite all tobacco being toasted, it looks like everyone else is just copying you.