Armor and elemental damage

If all spells defaulty target body, whats the point of lets say a monk having elemental resist armor on anywhere besides the body?

For one, because not all weapond default to target body.

So if theres no ranger and no warrior, then elemental defense in anywhere but the body is completely useless?

Not all spells default to chest, Magic missiles such as flare act similarly to arrows. Staves and wands also do of course, which can do significant damage with the aid of Conjure X. I remember a thread here recently where somebody was getting hit for huge damage by stoning, then realised it was because they weren't wearing a helmet.

Of course, elemental is still more useful on the chest than anywhere else. As a primary monk, I use +ele armour on the chest, and tatoos for extra energy everywhere else.