Only certain <i>parts</i> of the hardware responsible for key storage and verification are architected to be resilient against physical and electronic attack, but the entire phone is not.<p>For example changing the WiFi or Bluetooth MAC is not locked down and effects the UDID. Because the UDID was <i>never intended</i> to be a way to bypass the device encryption it was not designed with anywhere near the same level of care and sophistication as handling the encryption key itself.