I gave you guys Civilization last week or the week before; now see how it all began with Genesis.
The real question about monks is why are they wearing leather and not cloth? (And before you say anything about not adding an armor type for a single spec, consider holy paladin...)
Archetypal fantasy monks, like the kind you see in D&D or EverQuest or any other fantasy RPG, can wear leather armor. You have to keep in mind that these are warrior monks. We're not talking St. Francis here.
And spell plate is the reason why monks won't have a special kind of armor all to themselves. It's a massive headache.