You do have apps in the cloud, sort of. Apple keeps track of all the apps you've purchased. Instead of storing these files again and again for every person who purchased them they let you download it from the App Store again. This is what you see in the Purchased tab of the various iStores.
The content of that app (documents, game scores, whatever) may be stored in iCloud depending on the type of app, it's settings, and your backup settings. This is what you see when you go into your Manage Storage settings (under General > Usage or the iCloud settings)
http://support.apple.com/kb/HT4859?viewlocale=en_US&locale=en_US