We do not believe that, because AppleCare will be ready to support iOS 7 around September 10th, iOS 7 will actually be released to the public on or in the few days surrounding the event date. More likely, Apple expects questions about iOS 7 since it will be fully announced and demonstrated on that date. Apple typically releases major iOS updates the week following its formal announcement.
As in previous years, Apple is requiring most of its part-time staff to work full-time around the launch of iOS 7 to ensure proper support is provided to customers. However, this year differs in that Apple is also requiring a large number of hardware and OS X technicians to be trained on iOS as well. This likely means Apple is expecting a drastic increase in support calls regarding the new operating system.
The training material apparently focuses on the Find My iPhone Activation Lock feature which the company is hoping will be a theft deterrent. Other highlighted features include iCloud photo sharing, the redesign Camera app, Control, AirDrop, iTunes Radio, and improvements to Safari.
Notably, Apple is expecting customers surprised by the new design to call in for assistance. When this happens support staff are instructed to tell the customer that although the system looks completely different, it works exactly the same way.