Why can't I use my iCloud email address as my Apple ID
When I want to enter my iCloud email address (like foo@icloud.com) as my Apple ID, the system at appleid.apple.com tells me that I can't use an email address with a domain owned by Apple as my Apple ID which I find odd enough. I tried to create a new Apple ID through appleid.apple.com just to see what happens and even then it says that you cannot use an email address with an Apple domain.
It becomes even more odd when you consider that, if I'm not wrong, you can very well create a new Apple ID and use a new @icloud.com email address if you do it with an iPhone.
I can use my iCloud address as the primary email address of my Apple ID account so it's not a huge problem, but it still annoys me a little bit that the name of my Apple ID has to continue being my obsolete Gmail address.
Does anyone have more information on this?