I think this is key here. Before, you could try and lock or wipe your phone when it was stolen. But in order for it to work the thief must have let it powered on. If he was smart and shut it off, took it home and booted into DFU mode to restore a the thing back to factory settings, you were out of luck.

But with the new Activation Lock, it supposedly doesn't matter if it is shut down, the minute someone tries to flash the phone. Be it normally via iTunes or via DFU mode and iTunes there should appear a message that the phone has been wiped and must be unlocked with the iCloud password of the account that did the wiping. So no chance to flash the phone back to factory settings.