Positive law is man made law. The common law is the collection of legal case law that was used to interpret that law. Within the common law there is room for such areas as criminal law, civil law, tort law, administrative law, Constitutional law - each area of law uses case law and precedence to answer modern questions.
In the NBC issue, the court will use prior Supreme Court decisions to form their decision. That is how a common law system works - case law and precedence used to resolve legal issues.
And we listen to this guy why? The common law is the unwritten law of custom. Positive law is law created by statue by an act of a legislature. Postive (statutory) law overrides common law. As Scalia has remarked, there is nothing left of the "common law." Everything is statutory now.
We have a common law legal system. That is by definition a legal system where judges uses case law and precedent when interpreting the law. The principle.behind it is that the same set of facts should be interpreted the same way every time.
All those positive laws are interpreted in light of previous case law.
Why do you think that every Supreme Court ruling is a litany of prior cases?