So Apple could help make stolen iPhones useless to the thief by locking them, or they could be encouraging thieves who know they'll get a brand new one to sell on. More worryingly, this will invalidate your insurance:
Charlie Durrant was a victim of iPhone theft. After her handset was stolen last year she reported the theft to Apple and her insurer. However, when she requested a replacement phone, her insurer told her that one had already been issued in her name. The thief had taken advantage of Apple's lack of checks.