my emacs24 needs (require 'appt) in .emacs

I have updated to emacs 24 but now my .emacs file that was working OK with 23 is not working anymore

Warning (initialization): An error occurred while loading `/home/pmg/.emacs':

Symbol's function definition is void: appt-make-list

I had this entry in my .emacs

(add-hook 'diary-hook 'appt-make-list)

And from this mailing list entry I found the solution. I need to add (require 'appt)

;; from the emacs wiki -> calendar and diary                                                          
;; Mx-calendar -> d (show day) i d (insert task)                                                      
(require 'appt)
(add-hook 'diary-hook 'appt-make-list)
(diary)

And now all works OK. Why I did not needed before? I don't have a clue