just as Interface is much more than GUI, Interface Design should be much more than packing a visually pleasing skin upon some finished software product.

the interface of a system is critical to its usability, and high usability should be the main goal of its design. It explains a systems purpose and handling and should be understandable without too much previous knowledge.

Interface Design should be an integral part of the whole design and engineering process of a product. This especially applies when designing media.