Imagine that, somebody might subpoena you for evidence relevant to a legal dispute! Shocker!
A subpoena is a legal process and is not an invasion of your privacy. If you don't want it coming up in a court room, do not do it, say it, or write it down somewhere. Is this hard to grasp?
You know this is a good point, legally speaking. The way around that rule is the same as it always has been. Don't save incriminating evidence and plead the fifth. We're now living in an America where the average citizen is a criminal throughout his or her life, without always knowing it. It is only prudent to avoid storing information about yourself which need not be stored. And, we as consumers and free persons have a right to demand that we are in control. That we say if a device we buy can track us. He's just highlighting one of the many problems raised with being tracked without consent by using a device which does not advertise this behavior. And, you are giving a good booster to his argument. Your location can be obtained via subpoena and you didn't even know it was being collected. That is now true of every iPhone owner.
To understand a program you must become both the machine and the program.