RockYou's games are free to play, and you can play the game a for long time and with considerable success without ever dropping a cent into it at all, ever! However, you will have some limits placed on your experience. This game style allows you to choose exactly how much you want to spend on the game, and choose the features you want.
RockYou and the games we create cannot exist without revenue. Maintaining and improving our games requires the work of programmers, artists, GMs etc. All of whom need tools to do their jobs as well as a paycheck every two weeks.
We acquire revenue through selling in-game currency which in turn can be used to enhance your experience with the game beyond what is freely available.
This model allows you to enjoy your preferred experience of the game almost completely free of advertising.