I think the FBI is acting like there was a pre-emptive requirement for Apple to build a system to permit access.
The reason I say that, is that now that it has been proven the phone does not permit access, the FBI is trying to use a warrant to force Apple to break into the phone. But if providing access was never a legal requirement in the first place, why is it Apple's problem now?
Yes, only Apple can do what the FBI wants to do. In my mind, that should not be sufficient, in the absense of a legislative requirement, to force Apple to break a software system against their will--even their own software system.
I mean, let's say the FBI wants to run a sting operation against a gangster. Can a court use All Writs to force some random person to participate in the sting? I would think not.
Let's say law enforcement needs to pull a hard drive from a 30th floor apartment, without alerting the doorman. Can a court use All Writs to force a rock climber to climb up the building and go in the window to get it? Again, I would think not. Even if there was only one rock climber in the entire U.S. who could do what the FBI needed, it doesn't seem likely to me that an All Writs warrant would succeed against that person.
So why should it succeed against Apple? I mean, Apple is the only company that can do what the FBI wants--true. And they did build the phone to prevent access. But there was no requirement to build it any other way, so why would that be relevant?