Why the odd interactive form in byte-compile-file?

[Daniel Colascione <dancol@dancol.org>]

byte-compile-file begins with this interactive spec:

(interactive
    (let ((file buffer-file-name)
	 (file-name nil)
	 (file-dir nil))
      (and file
	  (derived-mode-p 'emacs-lisp-mode)
	  (setq file-name (file-name-nondirectory file)
		file-dir (file-name-directory file)))
      (list (read-file-name (if current-prefix-arg
			       "Byte compile and load file: "
			     "Byte compile file: "))
	   current-prefix-arg)))

Why do we go to the trouble of splitting the file name when we're in an 
emacs-lisp-mode buffer? If I'm editing /foo/bar/qux.el and type M-x 
byte-compile-file RET, this code has the effect of compiling qux.el and 
putting "qux.el" in file-name-history, not "/foo/bar/qux.el". Now, if 
default-history is something else and I use C-x C-f C-r qux, I'll end up 
on a bare "qux.el" instead of something I can actually use in another 
context.

Is there some deeper reason we're not using code that looks like this?

(interactive
    (list (read-file-name (if current-prefix-arg
                              "Byte compile and load file: "
                            "Byte compile file: "))
          current-prefix-arg))