Well...that's not how statistics also stack up. Because you are talking about individual results, not group statistics. Yes, every conceivable pattern has equal chances. Getting 100 heads in a row has the same chance as every 100 coin flip result, sure. But the chance of getting 1+ tails within 100 flips is much, much, much greater. Compound probability shows that getting 4 of the same thing in a row is significantly much rarer than getting different things, (as in a tails amongst heads.) It is more probable that Bungie hand picks which items to sell.