chronic snoozer,
a valid credit card is also one of the methods used here to obtain a boarding pass from a self check-in machine. However, if you have the booking reference a card isn't needed. Then again, what stops somebody from using a dodgy or just stolen credit card?(you can book an e-ticket flight half an hour prior to depature) There still isn't any mechanism to put a name to the face of the person requesting a boarding pass.
You just can't replace human beings with technology sometimes.