Surely the Apple Store would set up the new phone with his existing Apple ID, though? Even if they didn't, most people only have one e-mail address (that they know of?) and so will be forced into using the same account again whether they like it or not.
Just like the commenter at the same level, many times the customer would not bring in their previous phone and have little to no idea about what their email address even was.
The apple store will definitely attempt to gather that info, but at some point it is new account and have a great day!
You can create a new email address in the setup wizard. I know of people who set it up there and literally don't understand what they did, and don't attempt to remember it.
