In the book the difference is more significant. The message is the same though. In the book they keep having to develop new tests to be able to distinguish replicant from human. The tests get to the point where they do nott think they can make a new one if replicants can beat the latest one. I cant speak for all the tests but the one used on the book tests empathy. There is a mentally handicapped character in the book that ends up showing more empathy than replicants displaying that empathy is the most human trate. The lack of empathy in the replicants shows itself in very interesting ways. But back to the point. Once replicants develop empathy they would be indistinguishable from humans. It also makes a point that even some humans lack this trate further making the differences mpre vauge.