Let me use magic on bows and ammo in a 'flavor text' way.
A magical *Bow* is like having a heat seeker. The more magical, the more likely you are to *hit* the target, because it's 'Magic'. That shot paticularly difficult? Well, add a +5 to your hit roll; that's why it's easier to do wacky stuff in stories with a magic bow. Add that plus equally to the Force of the bow. The stronger the bow? The harder it hits.
Magical Arrows *cause damage*. Imagine a magical arrow that, if shot from a normal bow, shoots through armor. It goes right through it. Magical arrows Penetrate, when they get there. A magical arrow is like an armor piercing round. Thus, it does more Damage. The plusses apply to hitting (Going through armor) and going Deeper (Damage).
There.
That should offer some form of Arguement.
Now, seeing as we're in the Rules forum, someone should quote a page number.
A magical *Bow* is like having a heat seeker. The more magical, the more likely you are to *hit* the target, because it's 'Magic'. That shot paticularly difficult? Well, add a +5 to your hit roll; that's why it's easier to do wacky stuff in stories with a magic bow. Add that plus equally to the Force of the bow. The stronger the bow? The harder it hits.
Magical Arrows *cause damage*. Imagine a magical arrow that, if shot from a normal bow, shoots through armor. It goes right through it. Magical arrows Penetrate, when they get there. A magical arrow is like an armor piercing round. Thus, it does more Damage. The plusses apply to hitting (Going through armor) and going Deeper (Damage).
There.

Now, seeing as we're in the Rules forum, someone should quote a page number.