Greetings New Inspector -
Over my 30 years of teaching and working in the field I have received this question a time or two. In fact, it is kinda one of those questions that new inspectors have to learn by asking the question without being berated for it.
It is sometimes felt that the “grounding” or “equipment grounding terminal” should be down in order to it’s relation to earth. Well, that is a perception but is far from fact. In reality it has nothing to do with a lazy electrician, in fact I used to put the receptacles devices this way in rooms of dwellings where that was the switched receptacle to assist in furniture layouts and so on. Just something different I guess.
Now, in commercial installations it could be specified in the engineers drawings to be a specific orientation and in fact if this was the case it would have to be that specific orientation regardless of the National Electrical Code (which doesn’t care) because it was specified as such…thus the designer has made a specific statement of their intent.
Also in commercial applications where metal cover plates are used, it is commonly conceived that if the “ground” terminal is up and the metal plate works loose and slides down that it will have a less likely chance of “shorting” out the circuit than with the “ground” terminal down…so in many eyes, where applicable, it can be a design criteria that enhances the reliability of the circuit if deemed important to that environment to which it is installed…The facility owner and designer need to make that call in most cases.
As for the NEC, it does not care how it is oriented (with limitations to face up installations in counter-tops and so on, where applicable in Article 406)…
Hope this was helpful and provided some insight as to the myth.