certain shaman edges

Daevryn's comments re: Claim the Unfettered got me to thinking about some of the other shaman edges. Even when I had been "saving up" my edge points for a while, the edges "Sightbinder", "Cursebringer" and "Hex Augur" never showed up in my list of choices. I'm pretty sure I had perfected blind at that point. Is this another case of me being deficient in some stat? I ask because these edges are listed in both the "shaman edge list" and "necromancer edge list" help files. Are they maybe implemented in such a way that necromancers can choose them but not shamans? Or is it score one for the purple crack?