How do you know they didn't grind on VOG? How do you know they don't have 3 30+ characters? How do you know they don't do the nightfall 3 times a week. You don't. And I guarantee you there is a huge population out there that the RNG hates. Xur is some peoples only source of exotics because they have 5 Atheons epilogues and 7 aspects of glass. I myself have been playing as long as one of my friends. We grind out VOG and nightfall every week (we both were late to the dlc. Still trying to find our bearings for Crota) and I have 6 more exotic weapons that he does. Xur helps the guy that RNGsus craps on week after week. He is essential to this game to offset rng