I don't think it's the case at all. There are plenty of dog owners capable of rational thought who would save the stranger.
Human > Dog
It's really that simple folks. The dog may be "part of your family", but that doesn't morph it into a human. It's still just a dog.
Sorry my dog wins.. If it was your dog or human,, human wins.
Now if that stranger was a child I would save the child, if you want to through that in there.
I ran this stupid thread passe my wife last night, and said stranger or dog.. she laughed.