The Bicentennial Man - especially the novel - really does put this conundrum on its head. For those that haven't read it, it's about a robot that, through faulty programming, gets a will of his own (all robots in Asimovian novels are already sentient). He gets his own hobbies, a profession, owns his own property etc, but longs to be human. He becomes an expert at prosthetics and cybernetics and eventually has built himself a completely biological body. At that point, there are many humans who are more artificial than he is.
By Gottservants definition, he would at that point have to be defined as human. Of course, in the novel, he isn't - it isn't until he gives himself a finite lifespan by making his brain slowly destroy itself that the government formally declares him human, and the first bicentennial man - hence the title.
I think the novel aptly points out the problems with declaring that artificial beings are different. If we can create an artificial being, and if we can replace parts of ourselves with artificial prosthetics, then where do we draw the line? At what point does a human with prosthetics become a robot, and what makes a human different from a biological robot? Its origins? That's a meaningless distinction. Its soul? Before asserting that, we must show that the soul exists to begin with - otherwise that distinction is meaningless, too. So what, then?
