iOS 7 is taking security pretty seriously, with some updates to Find my iPhone that requires your Apple ID and password in order to perform a remote erase. This also applies to turning off Find my iPhone, making it much tougher to access should you ever lose it or have it stolen.
Once the device has been erased, a custom message can still be displayed on the lock screen. And, to re-enable the phone once its been erased, requires your Apple ID and password again. So, as Apple puts it, "your iPhone is still your iPhone. No matter where it is"