Virtual game economy is very unstable, and it changes constantly, even from server to server! Something like an expansion pack coming out can change the market drastically. Wow has around 200 servers + so you can get some idea of the instability of the market.
But...my father is a bit of a stocks and shares man, and really, is there that much of a difference between virtual economy, and market shares? He sits at his laptop selling shares all day. Sounds a bit like a hardcore gamer to me.
It's fascinating to watch an online game economy evolve. I've watched the WoW economy move from a handful of entrepreneurs playing the auction houses to most anyone having several thousand gold with little work. Of course, as in real life, inflation plays a big part in this economy and prices for goods have jumped as well. In another game, Eve Online, the developer has hired a full-time economist to watch and report on the trends in the game universe. He puts out quarterly reports on the state of the game. I've seen the spreadsheets and charts on this and it's literally the GNP of a country on display here. Raw and processed materials, sales of goods and services, industry fueled mostly by corporate construction of fleets of ships(Eve has corporations rather than guilds), shifting borders controlling the price and accessibility of materials, and hundreds of other aspects of an economy in microcosm. Of course it's a bit easier to track since all the game's players are on one server instead of multiple 'shards.'
Many European companies have their executives playing the game by creating a corporation, and seeing how they respond and grow (or fail) to the demands of the game world, so I think your point of real-world and virtual economies being indistinguishable will become even more true as time goes on. Even if you're not into playing these games, there is a fascinating subculture developing in front of us, where virtual goods will have a growing value in the real world.