I suspect there are exactly zero customers (of Apple or anyone else) who care to nitpick like this over strict adherence—out of the box—to any version of a UNIX

I suspect there are exactly zero customers (of Apple or anyone else) who care to nitpick like this over strict adherence—out of the box—to any version of a UNIX specification. Anyone who really needs to guarantee that their application will be immediately compatible with a new system is simply going to stick with whatever vendor they're already running it on and demand that vendor maintain bug-compatibility with their older versions.