And once you have every exotic and all your gear is 400 level you don't even need the infusion fuel 3oC provides. Xur becomes this sad old homeless guy with a bad skin condition who hangs around the tower on weekends hoping somebody will give him a few coins. Irrelevance is the fate of all NPCs in D1, some quicker than others. With D2 it'll be interesting to see if Bungie follows the same path or finds a way to make vendors and other NPCs relevant in the endgame.