Microsoft is about compatability. The sort of compatability in an Open Source world is nothing in comparison to the compatability in a Microsoft world.
Ever run Windows with Antispyware, used Office and Visual Studio for Office work, Halo and Age of Empires for Gaming, with DirectX of course, Windows Media Player for Media, MSN Explorer for browsing with the Internet Explorer engine for Rendering with Microsoft's Java Client for Java and Messenger for Messaging, Encarta for your Homework and all with Microsoft Update running in the background to keep it all up to date?
Now that is Compatability; everything working as one.
A Knight is sworn to Honour. His heart knows only Virtue. His blade defends the helpless. His might upholds the Weak. His word speaks only truth. His wrath undoes the Wicked.