> It might be true that you'll never fix a given bug, but shouldn't there be a record of the "known defects", or "errata" as some call them?

Yes, fully agreed. But closing a bug doesn't preclude that. A closed bug isn't refutation or denial of a defect. It's just an indication that there is no plan to fix the bug. Not every bug system works like this though. My bug tracker works like this, and I should have more clearly described what a "closed bug" is in my earlier posts.