At the moment, game companies control far more aspects of their world's economies than usually occurs to us. They certainly have more control over them than do the people who run real-world economies. No one sits in Washington and decides how productive your steel factory is going to be this month. They can influence it to a certain extent, but not very well.
The people who govern virtual worlds, by contrast, can tweak the rate of loot drops and the spawning of mobs and other resources whenever they want. The Department of Energy doesn't get to decide how much oil it's possible to take out of the ground. The designers of an MMOG, by contrast, can not only decide that, they can change it on the fly.
They also control much of the market. NPC prices rarely change in most worlds, and if they do, they don't change much. Any inflation is for the most part limited to the auction house and out-of-game sales. Power gamers and eBay buyers are the minority. Game companies generally won't reveal whether they take auction prices into account when tweaking loot drops and other factors. Even still, it's safe to say that in most worlds, these things don't have a consistent or significant impact on the broader economy (i.e., the parts that are run by NPCs and the environment - in other words, the parts that are run by developers).
A Roma Victor-like economy, though, is going to be much less stable. Besides being free to buy sesterces, RV players will also be able to set up their own in-world businesses, flogging the junk they've gathered, looted or crafted to their fellow players, or just buying low and selling high. By weaving players into the fabric of its economy instead of letting them float on top of it in an auction house or on eBay, Roma Victor looks to give gamers a much greater impact on the state of the world. In a place where players will be better equipped to compete economically with NPCs in supplying the items people need, players' choices are going to influence the course of the world and the gameplay experience to a much greater extent than it does in most MMOGs today.
As players of EVE and UO already know, making producers out of players means you've got to keep an eye on the market. I've got 660,286 units of Massive Scordite gathering dust in my hangar bay in the Piekura system at the moment because prices have dipped in the last week or so. I figure there's got to be a ship manufacturer out there who's going to get a hurry-up order soon enough, and when he does he'll put a buy on Scord again at the prices I like. I could get about 9 million InterStellar Kredits for it at the moment - but I'd rather get the 11 million I know it's worth.
For most gamers (that is, those who don't engage in RMT), the only interaction between their bank accounts and their virtual worlds comes in the form of purchase prices and monthly subscription fees. At the moment, your wallet is just a kind of on-off switch, where MMOGs are concerned. All you can do if you're broke is cancel one of your games. But if an RV-style pricing model takes hold, your wallet will soon be more intimately involved in your virtual life than ever before.
If you're paying $14.99 a month in a game like World of Warcraft, of course, you can just as well buy $14.99 worth of sesterces in Roma Victor every 30 days (provided you like the game). But what happens when the game gets rebalanced by a new patch and the leatherworker you've been buying from down the virtual lane finds that skins aren't dropping so readily as they were before? He raises his prices. Now you find yourself spending more game coin on the materials you need to make the armor you're selling out of your own virtual storefront. You try to raise your own prices, but since the company hasn't rebalanced leather armor, no one wants your stuff at the higher price. In a WoW economy, your only choice is to work harder for the coin you need to get your materials - the game still costs $14.99 a month no matter what's going on inside it. In an RV economy, however, you can work harder, or you can just spend a couple of extra bucks each month to cover your increased costs. To get the same gameplay experience out of it, you're now paying $17 a month.