They get away with it because it's all kids that doesn't know any better.

In literally all other games I know of the ratio is 1:0 since you can't cash out their in-game currency at all. Do you have any of example of a game or a platform where you can sell the in-game currency for the purchase price?

Secondlife have a fair spread and is player to player.

They take 3.5% of fee when you are transfering it to USD. (Sellers)

Buyers are charged charged a 7.50% transaction fee with a minimum of US$ 1.49 and a maximum of US$ 9.99 per transaction

------ The current spread on Lindex (SL Forex) is :

BUY: L$242 / US$1.00 (L$14,816 Remaining) SELL: L$249 / US$1.00 (L$29,411 remaining)

The closest I can think of are systems like Eve, where players can trade in-game currency for game time tokens purchased by other players. 1:1 ratio, but the real money is proxied by game time so that no one can actually remove cash.