I have dabbled with Windows Tablets over the years. It's not too hard to say what discouraged users from the early tablets: they were thick, they generated a lot of heat, they had limited battery life, they had horrible resistive touch-screens that could manage only one point of contact, and they were slow to respond.
But in my mind, the biggest drawback was the Windows paradigm of papers on a desktop. Until Microsoft came out with Surface, it really didn't apply to a touch device where the whole screen is your page. With Windows XP Tablet Edition, all Microsoft did was port Windows XP to a laptop computer with no mouse and a keyboard that could be called up on-screen. Trying to move Windows around with your finger was a pain (literally, it was a pain because you had to push really hard with your finger for the screen to register!)
I'm sure Apple had touchpad Macs in their labs, but until all the pieces were available like affordable multi-touch capacitive screens, LED backlit LCD screens that were easy on power-consumption, and an OS that could be ported to a new class of CPUs that were powerful and thrifty with the power usage so it could all be bundled together with a battery and no exhaust ports did Apple finally revolutionize the personal computing device landscape.
Windows 8 has the ability to take the existing SotA in tablet computing devices and be successful. Metro is a touch OS that people can use and enjoy. Download the demo from Microsoft and play around with it.
I am taken by the parallel of seventeen years ago when Apple had brought out the Mac and Microsoft was working on the first versions of Windows, influenced by what Cupertino had introduced to the world. Apple got rid of Steve Jobs and squandered the Macintosh, allowing Microsoft to catch and pass the Apple OS.
Today, Apple is once again in the lead with the iPad and once again finds itself without Steve Jobs. Microsoft is once again working on their answer to the paradigm shift in the market. Will history repeat itself?
I believe that Steve Jobs put the people in place to keep Apple moving forward, unlike before when his focus was too much on the Macintosh and not on Apple on the whole. But you know Microsoft isn't going to cede the tablet space to Apple or Google.