Developers being cocks? Sorry, I actually facepalmed when I read that. I take it you've never played an MMO? Gold selling thrives in MMOs because, at the end of the day, there is one fundamental truth that applies both in and out of game: (some) people are stupid. Gold selling has a noticeable and significant negative effect on the game. Sometimes this means they've got their bots out keeping a given zone completely barren of mobs, so that any actual players who want to do anything in the zone are unable to do so. Sometimes it means that the gold sellers flood the auction house with the items they have farmed up, meaning that any legitimate player who wants to sell some items for a bit of gold can't do so because the going rate for those items is so low that they can't turn a profit. On the flip side, the people who have bought gold now have so much money that the market price for other (non-farmable) items goes through the roof, meaning that honest players can't afford the things they want. Gold selling absolutely ruins the in-game economy, which makes the game a lot less fun for everybody, and that means the developers lose subscribers. That is why.
In fact, in recent years, things have got even worse. As the developers get better at spotting the behaviour of the gold sellers' farming bots, the gold sellers change tactics. Instead of targeting the game, they target the players - through various trojans and keyloggers and whatnot, they compromise a players account, strip it bare of gold and items, and then sell the proceeds on to other players. Of course when the player discovers this, they immediately go crying to the devs demanding that their items and gold be restored. The dev company then has to spend god knows how much on employing extra customer support staff to deal the player's own lax account security. That is a direct cost to the dev company caused by gold sellers. The claim that the developers are being cocks by protecting the interests of both themselves and the players is laughably ignorant.
Allow me to finish up with a little personal anecdote. An acquaintance of mine in WoW once had his account compromised by gold-sellers. I don't know how, since he's usually a fairly tech-savvy person, but everyone slips up once in a while. The gold sellers stripped his character completely clean, took everything he had, and passed it on. When he finally got his account back, and was waiting for his items to be restored, you know what his first response was? He went straight to the gold sellers and bought some gold, to cover what he had lost. Yup, he went to the very people who had stolen his (imaginary) gold, and paid them real money to get it back. And he never once made the logical connection that the people who had taken his stuff were the same people he was dealing with. The average person really is that stupid.
It's only a minority that actually does buy gold, so you can't even claim that "players want it". But when the developers have to fight an uphill battle against both the gold sellers and that stupid minority, so that they can improve the game for those very same players, you do have to have a bit of respect for what they do.