In actual fact, the majority of players don't spend much, if any money on in game currencies, and will instead put up with things like not having the best in game accessories or having to wait 24 hours for something in the game to finish growing or building before they can play with it. What there are, however, are the 1-2% of gamers known as 'whales', who will plough a lot of real money into your game, perhaps because they are really addicted to it, or because money is less important to them than time and a good gaming experience. Much as people will play things like pinball machines, which don't pay out, there is a certain amount the average person is willing to lay out on gaming entertainment, and for some that amount is high!