Is anyone else confused about why they are taking a percentage?
They own the servers, if they want a "percentage", they can just sell in-game gold, which they simply construct from thin air.
You have N players playing your game. If you sell imaginary gold, i.e. which has been conjured out of thin air, a certain percentage of the customers that buy it will get bored to your game very quick (compare to people cheating in games and getting bored), stop playing it and stop paying for it (assuming you have a monthly fee to play, like WoW). However, if you allow real-world money transactions between players, you have this group of players that farm for the items, which are loyal customers since they are making money out of the game, and thus, even though they lose some people because of the getting bored -factor, the loyalty of the farming customers outweighs that.
tl;dr: making people farm and sell the items generates more loyal customers = more long time-frame income for the company.
