No reason Windows can't have a great touch UI. Apple grafted it ontop of osx and Microsoft could do the same. I develop apps for iphone, windows mobile and native windows. The applicable APIs in each of the SDKs are much more alike then not. And with Windows Mobile 7, Microsoft is showing they aren't that concerned about a graceful shift for developers.
But the hardware to run windows can't compete with the ipad. The ipad is simply a screen, huge battery and one tiny circuit assembly. I use my ipad for days at a time without plugging in, not a speck of heat from the device, doesn't matter which way you hold it. It really is in a whole different class, truly beautiful. Compare that to the internals of any windows netbook or upcoming tablet. Packed tight with boards, small space for battery, and even a fan or two! Any device with a fan isn't going to stay on your lap very long, and will be easily blocked in the tablet form factor.
I'd love to see competitive hardware with Windows, got lots of industrial customers that would jump on that. The ipad has a huge cost/benefit increase compared to existing tablet hardware in use, and it's only going to get better. As it is now, we are struggling with an apparently dead end Mobile Windows 6.5, customers with hundreds of industrial devices. I'm hoping Android gives us another option for industrial/clinical applications, but haven't seen much indication yet. Everyone is just fighting over the smartphone market.