With regards to heavier limbs shooting a heavy arrow faster. If a bow with heavy limbs and one with lighter limbs shoot the same arrow, the bow with lighter limbs will shoot the arrow faster. Why would arrow mass make a difference? With both arrows the heavy limbs suck up more precious stored energy meaning there's less to go to the arrow.
Now you are asking the right question, Ryan. So why would arrow mass make a difference? Because the arrow constitutes 1/2 of the equation when we discuss bow performance..and like k-hat pointed out, the arrow 1/2 often times gets ignored. Here is my theory, albeit half-baked while I chased a ring on half an osage stave: Upon release of the string, an arrow imparts resistance to the movement of the bow limbs, proportional to the arrows mass. We talk non-stop about force draw curves of the bow (well, maybe we don't, but a lot of bowyers do), but what about the resistance curve of the arrow as it is being shot? It is not a straight line, there is a loading up initially as the arrow compresses and flexes behind the relatively heavy point/tip. A heavier arrow with stiffer spine and heavier point would impart greater resistance, particularly during the initial "loading up" phase. While a lite tip bow and a heavy tip bow of equal draw weight impart the same momentary force to the arrow, the heavier tip bow will have greater inertia, imparting more energy to the arrow through this loading up phase. Can anyone who actually understands physics evaluate that thought for me?