That's simple (hum) : the beginning is at the top, the end at the bottom.
It is this way that you read a text ; the first item of the menu is the top one, and so on.
The thing that is confusing is that the volume/progress bar is horizontal, and the touchpad vertical. Here is the logic :
Horizontally, left = before and right = after ; and left = less and right = more
Vertically, top = before and bottom = after ; but top = more and bottom = less.
So we finally end up in one case with left=top and right=bottom,
and in the other case left=bottom and right=top.
Mmmmmh pretty confusing indeed
PS : Congrats to whoever understands everything I say ^_^