The demand will only come when peoples none-touchscreen PC devices become outdated. In a world where many people still use XP with no problems, adoption to any new tech that MS introduce will be slow and gradual.
With Apple it is a little different since they make their devices obsolete a lot sooner and have much better marketing. Things probably won't kick off properly until Windows 9 or even 10 (providing Microsoft are going to release new versions of Windows on shorter intervals).
It could be a long time still for those computers to become obsolete. Those old systems remain perfectly adequate for the basic tasks that most folks use them for. And I don't think the computer manufacturers are going to want to wait for sales of these devices to pick up.
Also planned obsolescence could seriously backfire for Microsoft. Arguably the biggest reason for Window's continued popularity is its long support cycle. People trust that new and old applications will continue to work for many years.