Good point. The thing Cook can't say publicly is that once Apple creates FBiOS, every government around the world, especially the most oppressive regimes, will block imports of iPhones until Apple gives them a copy or they steal it from the FBI.

I believe the FBI is asking for FBiOS to refuse to run if the IMEI doesn't match a compiled-in whitelist, but my understanding is that phone thieves routinely desolder a chip to change the IMEI on a stolen phone. The FBiOS is for use when they have physical access to the phone, so I don't believe the IMEI whitelist is a large hurdle to get over.