The airplane analogy is a good one. Ultimately, if it quacks like a duck and walks like a duck, does it really matter if it’s a real duck or an artificial one? Perhaps only if something tries to eat it, or another duck tries to mate with it. In most other contexts though it could be a valid replacement.

Just out of interest though, can you suggest some of these other contexts where you might want a valid replacement for a duck that looked like one, walked like one and quacked like one but was not one?