Agreed, Ian...a dio conveys action of some sort, a viginette is merely a setting. These definitions as they relate to models seem to have sprung from the hobbying world of model shows and the categorical neccesities rather than from the de facto descriptions in the dictionary. In the dictionary, a viginette is described as "a brief scene or moment in a play or stage production..."
From what I've seen at shows, however, sometimes a viginette can be a pair of figures on a small base, even if there's an implied story. For instance, this scene--which obviously has an implied story--won a "Best Viginette" at SYRCON. So, go figure! If you're worried about entering it at a show, check with the club beforehand and ask what constitutes either in their rules