I'd like to have the uninstall-button as well, since it's better if the customers can uninstall themselves in an easy way instead of asking us how to uninstall or if we can do it for them. Also, it's better to do as much as possible automatically even if not everything may be removed, than doing the same thing manually.
DNP Developers: You might add an on/off switch for the uninstall buttons for the serveradmin to "activate at own risk". Of course, the end user has to get a warning message in some kind before actually deleting their application. In this warning message there could be some instructions as well, telling the end user that manually made changes they've done will not be deleted, and to delete those they have to use the file manager.