FrogReaver
The most respectful and polite poster ever
Let me give you an example. You can house rule that fireball works that way if you like. But it's a house rule. Nothing In The description of the spell says it does those things.
That's a cop-out. There's nothing involved anywhere in fireball that indicates that it is somehow magically discerning so as not to burn items on a target. "Because magic" falls flat in cases like this.
The rule was put there because players do not like to lose magical staves, scrolls and other valuable items to fire. It's a rule that makes no sense and exists for balance reasons.