The reason Apple went to the trouble was not really a marketing exercise, but rather because a lot of U.S. government contacts required it, or a waver. This is the same reason versions of Windows were also UNIX certified. In neither case did this certification actually make them more "standard" in the way that the rules originally envisioned.

So Apple's use of UNIX in marketing was to make sure they never ran into that as a disqualified on a government contract. My impression is that those contracts largely no longer require that (one small measure of common sense has caught up).