Again, this is basically the same as arguing that there should be no rules at all.
Other rules in the game actually accomplish those things. Taking the marksman talents lets your character make awesome called shots without penalty. Others let you gather information really well. There are plenty of rules that serve to empower player and character actions.
Encumbrance isn't one of them. What he's suggesting (quite reasonably), is that rules that serve only adjudicate problems between the GM and the players don't deserve space in the book. Rules that empower players and characters to interact with the game and the story - those are the rules that should be front and center.