Apple's myriad of logins and passwords is so frustrating to me. I had an iTunes ID for years and can't use it for anything anymore because it is not an email address. It is such a pain in the ass to do anything. I have two apple ids, an icloud account and a game center account.
The edge cases (10% of users who would use multiple icloud/gamecenter accounts) are making things a huge pain in the ass for 90% of users who are the only person that uses their iphone for app downloads, icloud, music and game center.