There is currently no way to disable following redirects. A patch to do so has been submitted recently, but I didn't see a good reason why one would need it, so I didn't add the option. Your mail is a good argument, but I don't know how prevalent that behavior is.
What is it with servers that can't be bothered to return 404? Are there lots of them nowadays? Is a new default setting of Apache or IIS to blame, or are people intentionally screwing up their configurations?