Not sure if I like the title of this question.

Regardless, if you play Farmville long enough you soon realize that the game becomes hard to play after a certain point without whipping out the credit card to buy a few bucks of the purchase/level up currency to help you get your farm humming again. The idea behind games like Farmville is not too different from playable game demos from traditional game makers, except that in this case you aren't asked to purchase something until you have invested maybe a month of your idle time in your farm.

People buy the currency because it provides them with entertainment in the same way that people pay to go to the movie theater. Sure they can probably see the movie for free in a few years when its free on TV, but being entertained has value to people too.