This is dependent on the application used to make the changes. Many
programs will save an updated file by first writing as a new file with a
temporary name, then deleting the original version and renaming the new
version. When that is done, the comments are lost. Wordpad behaves this
way. Notepad does not.
There doesn't seem to be anything you can do about this. Comments for
non-Office programs are actually stored as part of the NTFS file system.
Applications that are unaware of NTFS data streams will not be able to
preserve this information. Copying the file to a non-NTFS medium such as
a floppy will also cause the comments to be lost.