A lot of Massively Multiplayer Online games include a form of "premium" in-game economy that may be purchased with real money (cash) by the player, usually for the purposes of faster progression in the game or cosmetic upgrades. For example, there are Gems in Guild Wars 2 which are originally purchased with cash (but may then be traded in-game using the game's normal currency). Taking the example a step further, Hex: Shards of Fate (an online-only trading card game with similarities to Magic: The Gathering) has a "platinum" currency which may only be purchased using cash via the game's store, and is the only way of purchasing new booster packs of cards in the game. The developers have expressed that they want players to feel that their collection of digital cards has real value and the in-game auction house facilitates trades of cards, the rarest of which are trading for amounts in platinum valued up to about $100 each. The terms and conditions for the game state (as many other games do), and I'm paraphrasing here, that items within the game may not be traded for outside of the game for real currency. Not only does this make monetary sense for the developers, but I assume this is also to avoid a stack of legal troubles around money laundering and gambling/gaming laws in different territories.
However, Entropia Universe (wikipedia link) has as its key feature an in-game economy which is tied directly to US dollars, and specifically allows players to "cash out" of the game and back into real money. They have even gone so far as to produce bank cards which withdraw from the game and have now formed an actual bank to regulate trades.
My question is why are there not more games which take this approach of a game economy tied directly to real money? I understand that the economy needs to be carefully designed and balanced to avoid over-inflation (in-game) or other exploits leading to in-game currency being "created" from nothing, but the bigger concern seems to me to be the legal issues this would create. Given the amount of random chance involved in the game is this not effectively gambling? If so, how does Entropia Universe allow worldwide users without kicking up a storm of trouble from different regional authorities and governments? Surely this is exactly the kind of thing which is banned in certain US states (I am not a US citizen) or other countries. Is it because the game is based in Sweden and their more permissive laws allow for it? If so, do the laws of the country in which the player resides not take precedent?