Take a look at a melee cleric, for example. You need Wis for spellcasting, and Con for not dying, but they both use the throat slot using only the base items. With MIC, this becomes more of what it's supposed to (although it's strong even without that, it's the principle that matters).
Also in the MIC and Magic of Incarnum (and maybe somewhere else too?), both of which list body and torso as unquestionably distinct slots; although the latter uses "heart" and "soul," it still defines one as vest/vestment/shirt and the other as robe/armor.Have you pointed out to your DM that "One vest, vestment, or shirt on the torso" is quite explicitly a separate and independent slot from "One robe or suit of armor on the body (over a vest, vestment, or shirt)" according to the list of body slots?