An economy that mimics real life also mimics its problems - inequality, shortages/high-prices of desirable goods, lack of opportunities, little gain from hard work etc. The overall result might not be fun.I disagree with a lot of that. A game economy that mimics real life's free market aspect mimics its wealth of opportunities. Being able to initiate high risk, high payout business maneuvers is exciting. Being able to make long term plans is exciting. Being able to actually affect the market is exciting. That becomes entertaining gameplay by giving the player strong enough economic tools so they can concentrate on making interesting deals, instead of stupid busywork.
And it's easy to get started from zero. Most MMOs offer you a straightforward grind outside the player economy with which you can reliably build initial capital. Your virtual dude doesn't have taxes to pay or mouths to feed. Even if you drop down to zero, you can start again; failure isn't really risky. When you start doing business, there will be no patent troll lawsuit or overzealous government bureaucracy to bankrupt you. Most importantly, the participants in the economy are extremely loose with their money, because for the majority of them the entertainment of the game lies strictly in the sections where you get to bash dragons in the head; it's a heaven for a new virtual entrepreneur.
The opposite is the economies MMOs like WoW have: fixed plumbing, carefully designed to transport the bodily waste of the grind engine which is the game. The only "opportunity" you have is getting bored out of your mind camping the AH for the rare deal you won't get anyway because there are 10 other people doing the same, or constantly manually re-entering tens of sale orders for your bulk goods, with no way to even keep track of your inventory, profits and sales history, and no way to turn a profit that makes this worth your while.