I certainly prefer a simple rule so that I don't need to ask an attorney whether a particular API is copyrighted before I start working. But I found the origin

I certainly prefer a simple rule so that I don't need to ask an attorney whether a particular API is copyrighted before I start working. But I found the original article misleading in a few aspects, and wanted to clarify things before the discussion turned silly over misunderstandings. It's also true that courts are expected to come to the right conclusion for the right reason. If a company spent years telling people they were free to use some particular API, then sued them for doing so, it would be important to distinguish between a case where the API isn't copyrightable and a case where the API is copyrightable but that people had permission to create derivative works based on that API. For some reason, many people are unable to make that distinction when talking about things around the water cooler.