The simple pattern is a popular myth. For ex, you didn't list Longhorn (after XP) that was such a fiasco that after 3 years of development it was completely scrapped. This was an overly ambitious release with a new relational db filesystem (winfs), new graphics stack (avalon), and new networking stack (indigo). It didn't converge. The team forked Windows Server 2003 and rushed out Vista with as much of the intention (but not code) as it could from previous development. I was on the windows team from 98-11.