Backwards compatibility. I'm not remotely kidding here. There are still programs that directly parse these files instead of using Windows' APIs and the format i

Backwards compatibility. I'm not remotely kidding here. There are still programs that directly parse these files instead of using Windows' APIs and the format itself is fragile, and in the 90's the concern was more of disk speed access (where comments will slow down reading of registry files) meant that the designer have opted to not put comments (as you expect from that time that the manual is literally a book or a separate CHM or TXT file, with user comments stored at the "Notes" part of the book or another separate TXT file). It's similar to the binary DOC format pre-Word 97 which includes actual C pointers (so it's less of a document format and more of a snapshot of Microsoft Word memory). Edit: Some have noted Group Policy and its note field. I've disqualified that because it's not readily available in Home versions of Windows, because third-party applications are often not bundled with the necessary ADM/ADMX files necessary (which you might also want to comment), and the fact that the parent commenter disqualified the text-based REG files (which supports comments).