If arch linux doesn't include it, it's not a 'unix'; it's not even a good "not unix". So the author wouldn't have needed to correct his article but Arch would need to include 'ed' :)
I get where you're coming from but I just want to raise two quibbles:
> If arch linux doesn't include it, it's not a 'unix'
...but according to that version of SUS, I'm sure the original unix isn't unix either. In any case, I don't think you can just assume any particular spec when someone says the word 'unix', most people usually just mean *nix-family (and if the spec is relevant they'll probably cite it).
> it's not even a good "not unix".
I imagine arch is much closer to compliance if you install everything in the 'core' repository (which is recommended and includes ed). In any case, if lacking ed makes something a "bad not unix", I'm not sure most people mind being wrong ;)
then all unix systems have 'ed'
http://pubs.opengroup.org/onlinepubs/009695399/utilities/ed....
If arch linux doesn't include it, it's not a 'unix'; it's not even a good "not unix". So the author wouldn't have needed to correct his article but Arch would need to include 'ed' :)