I recently heard that they regulate the amount of money circulating in certain MMO games, which seems to me like a far fetched thing. Let us assume that you are a player in a game where you can kill monsters and gold is the currency. Each monster drops a set amount of gold each time you kill it, assuming that the monsters re-spawn, you could continue to pick up the gold dropped by each monster until you had an X amount of money.
Take Runescape for example. In your inventory you have 24 32-bit slots, each slot can hold 2,147,483,647 (or 231-1)gold pieces, but there is no limit to how many stacks of 231-1 gold pieces you can have. The only limit to the amount of gold you can have hear is the size of your banking account, and how many slots it can hold. In a member banking account, there are 516 spaces, which can each hold 2,147,483,647 gold, limiting you to 1,108,101,561,852 gold.
In another game, let us assume that monsters drop not just money, but also items. Let us also assume that there are shops you can sell the items too. If you kill monsters for said items and sell them to said shops, would you place limits on the amount of money said shops had in stock? What would happen when you wanted to sell and the shop had no money left to give you? In Fallout 3 (Which wasn't an MMO game but an XBox 360 game) each shop only had a set amount of "bottlecaps," the currency, and you supplied it to them by buying things from them. If they ran out of gold and you sold your items, then you would just give them away for free. If you were to incorporate this feature into an MMO game, then the result would probably be outrage from many players.
What if a game company were to add a feature which was more lifelike, where all jobs in the world were done by people. If you choose to run a shop, then you buy supplies from a warehouse, which is owned by the game company, and you cannot sell back to them. Assuming you made this game, this would be one way to help regulate money. Another way may be to add banks to a game that could loan you out X amount of money for your business, which you would have to pay back. This seems very realistic though, which may not be what people are looking for in a game (Though if anyone can produce this, I'll buy a copy ^.^).
Is there any real way to regulate currency in a game? I say yes, but from the games I've experienced, it isn't being regulated.