They are not greedy, it's part of their business/marketing plan. First, you attract people with low prices/low entry barriers and then you increase them gradually as time goes on and as your market share increases as well. It's what every major corp does in the real world too.
You also have to admit: Cryptopia making their own cryptocurrency, DOT Coin, and setting up their shop to receive DOT coins was a very good business move. It's creating demand for it, a lot of demand.
This is what we are doing with XBL, making our own cryptocurrency that will be used as time goes on, in more and more games by more and more people in order to create demand for it.