[johnday]

> Areas where centralization and high levels of security are important such as tax filing, flight booking, and online banking will likely use proprietary software for the foreseeable future.

Financial institutions, and government institutions, etc. will mostly be using proprietary operating systems for exactly this reason. By not teaching how they work (to a novice/intermediate level, not kernel specifics!) you preclude your students from taking most roles in such organisations. I'm not saying it's good that public services rely on private business, but it is naive to ignore it.