[dmix]

iOS and Android have labeled icons in a predictable order. The windows phone assumes the user is familiar with common phone app functions based on icons.

That assumes a lot from non-technical users.

Not sure why you brought up skeuomorphism. It's poor aesthetic taste but it doesn't necessarily make the UI difficult to use.

[freehunter]

Thing is, the user puts those icons there, not Microsoft. It comes with a few clearly labeled icons, and when you install an app you choose to put its live tile on the start screen if you wish. With that in mind, it should be fairly obvious to the user which tile does what.