A novel product may well be covered by both a utility patent and a design patent. The design patent will only protect the novel, ornamental features of the patented design, not its function. In case of US Design Patent D710181 it seems odd though. The hinge body itself seems pretty standard. One may assume that it was designed to match that of numerous other hinges, as to fit the same cutout template in the door and wall.
That leaves the step in one of the hinge elements, which obviously serves the function of limiting the maximum range in which the hinge can be opened to about 90 degrees. That step, however, is functional. And there appears very little the designer could do about the functional aspect of the step that was subject to ornamental variation: Changing the angle of the step would interfere with it’s function. The height of the step is likely also selected primarily based on functional considerations. But anyway: The application made its way through the USPTO only with a typical examiner’s concern related to the drawings, not the design itself.