Enter daily quests -- with just a few minutes effort, players could cash in and pick up a nice chunk of gold. And with the coming of patch 2.4, daily quests are everywhere. Do an hour of quests and you've easily got sixty gold, do even more and the gold starts pouring in. Which means the reasons for gold buying and selling are shrinking. Of course, it won't erase gold buying completely (some people will always cheat, no matter how little effort it takes them to earn the gold legitimately), but the barrier to earning more gold is lowered that much more.
But, says Relmstein, the Federal Reserve's control is a two-way street. Once you start pouring too much gold into an economy, then you have to start dealing with inflation. He expects that the Sunwell dailies will start to disappear from the game as of Wrath, because if not, then Blizzard will have to go the other way to control inflation: raise prices. Think 5,000g is a lot for a flying mount? In the future, if the amount of gold in the game stays the same, it may be even more.