There is much more to game development than design and programming of the actual gameplay. As any other application it is important that the interface around the game is both appealing and user friendly, and functionality like highscore, gamecenter integration and game economics, are just a few of the technical challenges of the whole package around the game
Every functionality is included in user tests, to make sure that users can understand functionality and navigate. Selections of the game levels is testet on users to find out what users consider fun and to reveal parts of the gameplay that is not working as intended.
We go back to work weeding out the bad and creating more of the good stuff.