Similarly though admittedly more permissive, with Amtrak iirc it's like: you need a credit card and they probably won't check your ID. There were several more years after 9/11 before the "papers please" principle came for the trains and buses too.
E.g. search turned up a claim Greyhound "employees are not allowed to sell a ticket without an official ID" https://travel.stackexchange.com/questions/140703/i-have-no-...