I believe this is not a difference in naming of KStars, but of a setting on your computer. All the programs have a .app extension. Whether or not you can see it is a factor of whether "hide extension" is enabled for that specific app or system wide. On my system, the same programs you showed in your screenshot show .app at the end of their names. You can right click on the KStars.app bundle, click "get info", and then check "hide extension" Or I think you can also set this systemwide.