In addition to the "drawstring" which keeps...
In addition to the "drawstring" which keeps the top of the pack closed, there are two additional cords which don't seem to do anything (they don't tighten the back in anyway, they're just kind of attached to the bag as loops). What are these for?
They're compression straps. They're there to cinch down the body of the pack so that you don't have dead space/to make the pack smaller.
@Thomas Ogasawara - not sure we're talking about the same straps. I don't' mean the flat ones with the clasps (that you can see in the photo above). These are just two "loops" that hang off the bag, near the drawstring. They would fit around your wrist or so, and are the thin (maybe a couple milimeters) circular cord.
It's as if they took cord, made a loop, and attached one part of the loop the bag and let it hang. I don't see how they could be used to tighten anything. Are these what you mean?
I believe you're referring to the ice axe/pole loops. The head of the ice axe/tip of the collapsed pole sits in the flat loops on the bottom, and the shaft is held against the bag with the bungy loops that are near the drawstring. It's just short of a good design: most packs with this same setup have a little hook on the bungy loops that make this a lot easier (e.g. Lowe Summit Attack 30).