Apple has informed developers that the upcoming Mac App Store willn't support two of its major iOS App Store features: "Game Center and in-app purchases".
In-app purchases come in handy for developers that want to employ a freemium model for their apps, by not requiring an additional download if the user decides to pay. In-app purchases are also being widely used in games for enabling people to buy virtual goods from within the games.
And speaking of games, Game Center, a feature that was introduced to iOS in version 4.1, is also not going to make it to the Mac App Store. Game Center brings a social side to gaming, allowing you to compete with your friends in compatible games (even in live playing sessions), unlock achievements and move up the leaderboard.