The reason you don't believe in that sort of "fairy tale" is because you don't hear about those dogs in the news. For instance, you'd think that you're taking your life in your hands every time you get into a car, since all you hear about on the news are traffic accidents.
I know of 2 pit bulls (real ones, American Staffordshire Terriers) who are wonderful pets (well one still is, the other was killed by a car. In both cases, they're well trained, and have terrific dispositions. Maybe part of it is that they were purchased through reputable breeders. The surviving dog would probably show a burgler around the house, pointing out the valuables, all for a scratch behind the ears. BTW, that house has the one dog and three cats. The dog plays with 2 of the cats, and is terrified of the third cat.
Mark
I was careful to include strangers and the accompanying interaction. Their are very few animals on this continent and most on the others that I'm not familiar with. Those dogs you're talking about would have gotten upity in the situation posed.