But then you go on to speak of edge cases that precedent can't deal with, but I would argue that your view of case law as essentially "algorithmic" is flawed. Obviously precedent cannot be exact, but using prior interpretations helps guide thinking.

For example, look at Katz v. US, one of the seminal cases that would inform this case. In Katz, the court starts with existing law, one that prevents illegal searches, and tries to decide whether that law can apply to electronics (such as tapping a phone). At this point the OCCSSA is in effect, but not really tested, so we've got a pretty fuzzy legal area despite the fact that phones are a well established technology. The court rules that even though law enforcement did not search or seize things, that privacy is still implied in electronic communications because of other acts a user takes surrounding the act of making a phone call (closing the door, making the phone call from home, etc.).

In fact, there's a whole legal concept at work here called lawful intrusion that is built upon every time a case is judged. These concepts, and human application of them to the case at hand, help attorneys, judges and juries deal with edge cases.