According to TechCrunch, the new policy is designed to unify user actions within Apple's ecosystem, provide better customer service to people visiting the Genius Bar, and cut down on no-show appointments.
An additional reason for this change, we understand, is to give the control of a Genius Bar appointment to a user directly, who must know their credentials and enter them before being able to confirm a payment. There is also the convenience of having a customer's data automatically filled out with a simple entry of the Apple ID. This should allow Geniuses to reference past purchases and access warranty info and dates much easier as well.
Along with the Apple ID requirement, Apple has been making other significant changes to its customer policies in recent months, launching a redesigned AppleCare website with 24/7 live chat support in August and implementing new AppleCare+ fees earlier this week.