HT4759: iCloud: System requirementsLearn about iCloud: System requirements
iCloud doesn't sync your apps. An iCloud backup backs up your app data (which is the setting you were looking at). Also, restoring to an iCloud backup recovers the app data and redownloads the apps from the app store.
If all you want is the apps, you can either sync them from your iTunes library or redownload them for free. Also, if you turn on Automatic Downloads for apps in Settings>iTunes & App stores, when you purchase an app on one device it is automatically downloaded to the others (assuming they are all using the same Apple ID).
However, if you want your apps and app data, you would have to restore your devices to the entire backup of the device that has the apps and data you want.
1. Make sure all your devices updated to iOS 6 or later;
2. Make sure all devices' General Setting "Use iCloud" setting in ON;
3. Make sure to set the time automatically to all your devices;
Mac OS X: System Preferences > Date & Time > Set date and time automatically
iOS: Settings > General > Date & Time > Set Automatically
4.Make sure that your all your devices has enough memory under iCloud.