In order to support Sky Burger in the latest version of iOS we can only support devices running iOS 4.3 and newer. This is based on Apple's choice to drop support for these older devices within the latest version of their developer tools. You will probably run into this issue with other apps unfortunately.
You can still continue to run an older version of Sky Burger on your device. If you have deleted an older version of the app from your device and want to reinstall you will either need to restore your device from an iTunes backup from before you deleted the app or, if you have the older version downloaded in iTunes you can reinstall that onto your device as well. When iTunes installs an app from the store it adds a special key that allows your device to open it. Which is why we cannot just send the old version out to players. Only apps which are installed from the store can run on your device.
Please see the following link for more info on restoring from backup: http://support.apple.com/kb/ht1766