Google has increased the App limit in the Android Market from 50MB to 4GB. This would let the app developers to upload high-quality 3D interactive games of higher size easily. The size of your APK file is limited to 50MB to ensure secure on-device storage, but expansion files can be attached to the APK.
Each APK can have 2 expansion files of 2GB each which is 4GB that would be hosted in the Android Market to save you the cost. Users can clearly view the file size before they install or purchase the app. The 15-minute refund period will not start until the expansion files are downloaded.