I wish we wouldn't have posts like this that are just idle speculation about an area about which a good deal of expertise exists (virtual economies are built the way they are for a reason that generally has little to do with bits and bytes; there is plenty of specialized vocabulary about this, as DanielLC points out). Good posts should at least acknowledge that the expertise exists (which requires a bit of homework), and maybe explain some of the concepts if they are worth learning.
The vocabulary he linked to originates on tvtropes, not with anyone who has actual expertise in regulating game economies. There may be people with considerable expertise in this field, but if so, I doubt that's the jargon they use, unless they picked it up from tvtropes; we certainly didn't pick it up from them.
I do find it a bit hilarious how badly the economy of Neopets is managed. The administrators are completely blind to the realities of the system they've created, and the prices of goods on the site had increased in a range of one to three orders of magnitude while they were still reporting inflation levels in the single digit percentage range.
They regulate money indirectly by changing the proportion of Money Spiders and Money Sinks.
Also, money can be regulated by having a closed economy. In other words, don't have Money Spiders or Money Sinks. Just make the spiders' guts useful for something, and have people sell it to other players. EVE Online used to do this, but they stopped.
Reality is a tool, not a feature. Real-world economies optimize for the productivity of the participants, whereas game economies optimize for fun of the participants, instead. Part of that is giving players a sense of progress, and hyperinflation helps with that goal.
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.