That silvery split ring is called a compression ring; it wedges between "bearing cover" and fork to maintain headset adjustment. Although I've read and worked on some threadless headsets I've no experience on your particular model; on the onesthat I have, that gap is seen and it is just cosmetic. If your headset is not indexing or too loose, then everything is as it should be. But please wait for any of the more knowledgeable people from the forum chime, in just in case.