I believe it is written the way it is because the stealth skill can be used in several different ways. For example, the Cameleoline Cloak is only useful when a PC is trying to be totally unseen. It wouldn't apply to Shadowing, which has little to do with blending into an environment and more to do with blending into a crowd. In the crowd case, a cameleoline cloak would be something that makes the character stand out due to its nature. And how does the Stummer, a sound deadening device, make a character harder to see? It doesn't. It makes him harder to hear, which is totally different. I'm fine with the items as is for the reasons I've listed and other similar situations. To put it shortly, specialist stealth items only make a PC better at one particular facet of the skill, not all of them.