Is Windows Vista the last Windows version ?

Remember when Microsoft announced that IE6 was the last version of IE, meaning that all future enhancements would come as additional components, rather than as a complete new version ? (OK, I hear you, they changed their mind since then. But it was only because the market pushed hard enough).

Remember when Microsoft announced WinFS, Avalon and Indigo as the next big things that would make up Longhorn Vista ? Then they said that WinFS would come later. And they said Avalon and/or Indigo would be backward compatible with earlier versions of Windows.
If they can be plugged in later and they can be made backward compatible, it means they are components, right ? Then why do we need a new version of Windows if all major new stuff is a set of components ?

Why do we need a new version of Windows to solve the today's biggest consumer problem : Making the Internet safer ? It's all about releasing enhancements of IE and Outlook (Express).

Also, it would make it much easier to release quality software : Don't ask everyone to be ready on the same day. Allow each team to release sooner or later.

No, really, who needs a new version of Windows ? I mean... except for Microsoft ! Because making people pay for components is another story...