The exotic buffs come before the Dark Below expansion's release. (Dec 9) Just because they aren't fixed yet doesn't mean they are ignored. The fact that people ask for Gjallerhorn each week is probably why it isn't frequently sold by Xur. I doubt they want what happened with Suros to happen to each widely effective weapon. It's obvious that Bungie takes a descent amount of time testing things before they add them; DeeJ replies to almost every petition stating that he saw it and that there was no need for it being a petition.