"Though Demon Hunters can shoulder heavy mail like any other warrior with an eye towards survival, their acrobatic movements incline them towards lighter gear. Cloaks provide chest protection without trumping mobility."— Game Guide(src)
Contrary to the lore entry, Cloaks offer exactly as much protection as any other Chest Armor. However, in addition to the stats of those, they can also roll Hatred regeneration and maximum Discipline.
A Cloak may be transmogrified into a normal Chest Armor, but only a Demon Hunter can do the other way.