I've seen a lot of CEO and ED positions advertised in magazines over the years. Usually they are in an upscale classified ads section near the back. I can't speak to why an organization would or wouldn't do that as opposed to a discreet approach, but internal candidates would know either way.

Maybe it's something similar to what they do in the ivory tower where they have to show they are looking for candidates in all sorts of different places beside internally to combat cries of nepotism and favoritism? Maybe that's overthinking things?