Why didnt wordpress include parameter in the save_post action refernce?

Why didnt wordpress include parameter in the save_post action refernce?

http://codex.wordpress.org/Plugin_API/Action_Reference/save_post
Why Wordpress didnt include $post and $post_ID parameter and their
function. I realise these parameter exist only when I checked the source
code, What these parameter actually do?? Don't you think that they need to
include every parameter in the action hook reference so that we can assign
action to the hook