(meaningful) isn't as much a get-of-out-jail clause here as you suggest, if I understand correctly. Requiring implementations at all, even if they are broken, moves the time when you find out about a missing definition to runtime, rather than being statically determined at typecheck time.

If the not-overriden method isn't commonly called, it's possible for the non-meaningful / raise an exception version to make it to production. Not so if the error happens at typecheck time.