They are planning to implent Bitcoins, should've mentioned that, but indeed it's not there yet.
You can pay to play the game more intensively, which is how they make their money. You should read their explanation of the game and the system, it's actually quite interesting!
I'm not in a need for such a game, but whoever wants to do that should read that very carefully.
I kinda get the snowballsystem vibe from it.