I once read some social psychology article that could relate to this. It explained how we don't actually see other people as full individuals unless they are close to us. The milkman is the guy who brings us milk, and even if we know he might have a family and a life of his own, he is nothing more than the milkman to us, because he is not in our inner circle. We see them as jobs or simple links to other people or places.
Pets are more than wild animals. Most people form a very strong emotional attachment to their pets, and they might even love them more than they love another family member, so it's no suprise most people would choose the lives of their pets over "the original poster".