Microsoft has been unusually protective of Windows 8 and ships it with wallpaper that says "shh... let's not leak our hard work," a clue that it fully expected someone to try and leak the new OS.
Windows 8 may also have a range of features that aren't ready to show to outside of Microsoft. Separate development versions known as "red pill" builds make a licensing check to see if it's a Microsoft employee or someone else cleared to see all of the new Windows 8 features. Without the code, they only see relatively 'safe' features. Most of the publicly leaked builds are from branches of Microsoft's build process that don't contain a specific DLL required for loading a number of new Windows 8 features. It's understood that certain branches of Windows 8 contain extra components that activate with a specific Windows key. It's believed the full Immersive tablet interface is visible when the red pill code works.
Even though, Microsoft's next-generation Windows has seen a large amount of leaks recently. Which, now resulted in two full time Microsoft employees have allegedly had their employment terminated due to Windows 8 leaks.
Canouna, a well known leak tracker, is now claiming that two Microsoft employees have been fired due to the recent leaks: