So there is really no reason to hold a holy symbol in one's hand? It seems that wearing it frees up the hand for other things.
I'd like to add that the reason the rule is written in this vague, confusing way, is of course that clerics presenting their holy symbol (read cross) to the baddie (read vampire) is a strong cultural icon.Exactly.
As has been pointed out, the RAW specifically says Holy Symbols are worn (unlike other implements, which must be carried in your hand to function). Since the RAW does not specify where you must wear your holy sysmbol, holy symbols do not occupy one of the standard "item slots".
It wouldn't make sense to institute a "holy symbol slot" if that prevented clerics from occasionally using their hand to hold their holy symbol.
That, and the fact such a slot would be the only "abstract" slot with no specific physical location. All other slots have a place on the body; holy symbols are much more freely held or worn.
So while, yes, in practice, there is a holy symbol specific "slot", this is not official...
...regardless of how the CB programmers implemented it.