iOS is a shrunken version of OSX, while Android is a barely shrunken version of Linux. Aren't all modern mobile platforms shrunken versions of desktop operating systems?
The relationship between Windows Phone 8 and Windows 8 is closer than that, though. My understanding is that both will make calls to the same WinRT APIs, meaning a significant amount of code (and the XAML defining the UI) can be shared between both platforms. That's a very different relationship than Mac OS has with iOS (where the UI differences are significant) or Android has with Linux (where there is almost nothing in common between X and Android's UI).