More specifically, this is an implementation of Enhanced 911, Phase 2. Support for Phase 2 will be required in the US next year.

911 service has gone through a few different capability upgrades.

Basic 911: You communicate the nature of the emergency and it's location by voice.

Enhanced 911: The call center receives your landline phone number and looks up your address from a database.

E911 Phase 1: The call center receives the mobile phone number and the location of the cell tower taking the call.

E911 Phase 2: The call center receives the mobile phone number and the phone's location.

http://www.marioncoks.net/Departments/EmergencyCommunication...

Apple is simply implementing the new standard here.