An Apple ID is the login you use for just about everything you do with Apple, including using iCloud to store your content, downloading apps from the App Store, and buying songs, movies, and TV shows from the iTunes Store.
An Apple ID is your user name (Google+ profile across google services) for everything you do with Apple: Shop the iTunes Store (playstore), enable iCloud on all your devices (google+ backups), buy from the Apple Online Store ( Buy Google hardware from the playstore), make a reservation at an Apple Retail Store, access the Apple Support website, and more ( and more ugh). You are required to have an Apple ID for Facetime, photo stream, Apple email and imessage. Google requires a Google+ profile for Hangouts