I have no way of knowing, but I would guess Microsoft expects Windows 8 to be adopted by Surface/tablet users first. Windows 7 will be the enterprise desktop of choice for some time. If things go according to Microsoft's plan, a few years from now users will be comfortable with the UI formerly known as Metro. Then the enterprise will migrate to Windows 9+ with whatever refinements it has. Whether this works or not, we shall see.
That makes logical sense except for the fact that after windows 8 ships you won't be able to get a regular desktop with 7 in the normal routes. They positioned it wrong for that.