Windows 8 is going to be a "true" tablet platform that provides first-class support for touch-based tablet systems. But not everyone wants a tablet. Lots of us use PCs and are happy with our mice and keyboards. We don't have touch screens, and even if we did, we wouldn't want dirty fingerprints all over our monitors. Are we going to be left behind by this brave new world of the post-PC?
Windows 8 will be a tablet operating system. But it's also an out-and-out PC operating system. The PC still matters. The PC is still a core platform and PC users are still a core demographic. PC applications are never going to disappear, and Windows must continue to support them.
Windows 8 will run existing Windows applications on a regular Windows-looking desktop. It will, of course, support mouse and keyboard input—and pen, for those rare people who want to use styli—and for regular Windows applications, nothing much will change.