When I used to do a lot of windows programming in the late 90s, I wish that I had a sensible guide like this for handling strings. TCHAR was always a source of subtle bugs.
I suppose, though, that the underlying problem was that Microsoft was so late to implement a compatibility solution for Windows 9x. Most software of the time ended up implementing on "ANSI" multibyte character set (MBCS) just because otherwise you would need to either deploy 2 executables or do your own thunking. This solution would be a double thunk on 9x because you'd be thunking your UTF-8 to unicode and then thunking that back to MBCS.
I suppose, though, that the underlying problem was that Microsoft was so late to implement a compatibility solution for Windows 9x. Most software of the time ended up implementing on "ANSI" multibyte character set (MBCS) just because otherwise you would need to either deploy 2 executables or do your own thunking. This solution would be a double thunk on 9x because you'd be thunking your UTF-8 to unicode and then thunking that back to MBCS.