The following were set as requirements for apps on the Windows Store for Windows 8
- The application will need to give users the ability to navigate using touch and gestures.
- The app should provide the same user experience on all processor types. If that is not possible they need to submit a version of the app for each processor type and specify the differences.
- User should be allowed to install a purchased application in up to 5 devices simultaneously.
- Developers must offer users protection against unintentional large data transfers.
- There will be no cooling off period to return apps due to accidental purchases. except where required by law.
source - Slashgear