As a victim of an iPhone theft - it was literally ripped out of my hand on a very public boulevard - I was grateful to be able to remotely wipe it within hours. I am even more grateful now that it will require a passcode within 12 hours if it doesn't get a touchID, and I really look forward to the day that "wipe and make unable to be re-authorized except by taking it to an Apple store, and also mark this phone as stolen" will be built in to "find my iPhone".

Since the phone hardware will only run software signed by Apple's private key, Apple can make a stolen phone effectively unusable. You need to have a key to put it in recovery mode, and even with signed software the hardware ID won't change, so the only signed code could be code that will check the hardware during the authorization process (I think this is already happening for anti-counterfeiting purposes.)