This is like saying that if /web/index.html exists we shouldn't return 404 when /web/junk.html does not exist. That's clearly nonsense and not how http was designed to work.
I should have been clearer about this relating to HTTP RPC. I updated the post.
That said, after reading the responses here, I can see that what I've actually achieved is making the response harder to determine for the client, which is antithetical to the objective.