I've observed similar things to happen in other tools too - third-party tools that will list a certain set of file formats by default, and enable Autodesk formats if C:/Autodesk is present.

It seems to be most common in systems that cross major business domains (or come from completely separate companies). If you could just add an entry to the featureful, versioned, controlled config file then you'd do that, but if you can't developers frequently resort to the "does this path name resolve" heuristic.