A member of the Windows Vista team explains (via Joel Spolsky):
I worked on the "Windows Mobile PC User Experience" team. This team was part of Longhorn from a feature standpoint but was organizationally part of the Tablet PC group. To find a common manager to other people I needed to work with required walking 6 or 7 steps up the org chart from me.
So after 12 years, you still have to go to the Start menu to stop the computer.