Re: Why is not end-of-defun-function buffer local?

[martin rudalics]

> More specifically, the problem is to decide *when* to make a variable
> buffer-local.  I.e. Setting the variable via `setq' should make it
> buffer-local, but setting it with `let' shouldn't.

Has this to be carved in stone?  Why should with

(defvar foo 1)
(make-variable-buffer-local 'foo)

the form below not set the default value of foo

(let ((foo 2))
  (setq-default foo 3))

and the following form

(progn
  (setq foo 4)
  (let ((foo 2))        
    (setq-default foo 3)))

set it?  Isn't code depending on one or the other behavior silly anyway?