Gartner says even Microsoft can’t support the cost of monoculture:

Vista will be the last version of Windows that exists in its current, monolithic form, according to Gartner.

Instead, the research firm predicts, Microsoft will be forced to migrate Windows to a modular architecture tied together through hardware-supported virtualisation. "The current, integrated architecture of Microsoft Windows is unsustainable – for enterprises and for Microsoft," wrote Gartner analysts Brian Gammage, Michael Silver and David Mitchell Smith.

Windows Vista the last of its kind By Matthew Broersma, Techworld, 25 August 2006

The dinosaur has gotten too big for its environment, so big it’s become too difficult for enterprises to migrate from one release to another, and it’s too hard for Microsoft to release regular updates, or even patches. So what’s an overgrown dinosaur to do?