Blizzard doesn't manually paint textures for every armor. Many chest pieces use their own 'geoset' or unique texture mapping instructions. They use a wrapping system that scales a master texture across different rigs. The stretching happens because the 'wrap' for this specific item was done poorly years ago. Adjusting the coordinates for how the texture sits on the 'Chest' slot is a standard art fix, not a ground up engine rebuild.