It doesn't work well on a tablet, IMO. Even if you think it does, operating systems like that on the Courier and the iPad work better for those devices. Windows WORKS on a multi-touch device, but it does not WORK WELL on a multi-touch device, at least not compared to the other options. If you want to trade and endless amount of programs and features (99.9% of which don't even take advantage of multi-touch in any way) for a proper multi-touch interface, that's your decision. But most people don't want to run Windows and encode a video on their tablet-like device. They want something tailored to their needs. They want to cut out part of an image and flick it over to their project in a way that feels natural.
Most people don't mind application stores at all, or not being able to install patches to change their interface, or whatever you want to do. Most people are happy with the way it is. Even if you're not, you can always jailbreak your device. You know what you're buying when you buy it, and if you don't want to buy it, you don't have to buy it. The very fact devices like the iPad and Courier appeal to so many people shows that the designers are doing it right.