The thought of video game economies have fascinated me ever since I got my hands to playing EVE online. I have seen how creating a 'real' economy is not only beneficial for a Massively Multiplayer Online (MMO) video game but is also integral to the game concept. Recently, a friend of mine and I had a brief banter about this very topic; he mentioned how the traditional gold system ever present in MMOs is just as similar to Path of Exile's 'economyless' economy.
Being the ever-militant devil's advocate that I am, I immediately pointed out how this is not the case. While during the course of our conversation I have blurted walls of text about my observations with Path of Exile, I will not burden you with the same pain and I'm going to condense the thoughts that I was having at that moment.
One of the reasons why Path of Exile, I believe, is such an important experiment in video game economies is with how it treated the idea of money. Traditionally, money in videogames are almost always standardized. Gold, gil, G, GP, ISK or whatever form it may take. It is always this value that you constantly get which sole purpose is to be the medium of exchange between players and non-players alike. While it might make a lot of sense for someone to have such a mechanic in games to facilitate trade, going for that solution might not always be the right answer.
Using a standardized form of exchange constrains the value of items and services in that one currency and in doing so centralizes the creation of such value. Should the economy be 'well controlled' with money going in as fast as it goes out, the rate of inflation within that system can be minimized. But any slight variations in attempting, or not attempting, to do so, will invariably cause great changes, such as having markets with items that are extremely overpriced to compensate with the excess amount of gold within the economic system of a video game.
What Path of Exile did, however, was to remove this centralized medium of exchange and created a more informal economy with no fixed unit of value. This way, it allowed for the players themselves to construct value out of things that they get within the game, with items that are harder to obtain having more value. These 'valuable' items became the units of exchange within that game system and, ultimately, a de facto standard. In my opinion, this development alone could have answered the issue that brought up earlier but the game went one step further, as these items were also valuable for their effects, of which when used consumes the item. This helped further curb the rate of inflation as there are more ways that 'money' can be removed than being put in.