You were rewarded those strange coins for something you did, you wanted an Exotic and Xur had the one you want. Bungie didn't put him in there for no reason at all other than to piss you off, they probably put him in there to ease the pain of RNG on most. I mean, it's been about 1 month since my last RNG exotic (recently got TLW from a ROC after seeing someone pull a MIDA 2 strikes prior, but, that's not the point.) Point is, if it's there and that's how bungie wants us to play their games, then, it's fair game.