Don't disagree with you on the iPad being like a glorified DSi, although I think it's better described as a *really* big iPod Touch :)
That said, and as someone who is pretty happy with W7, I couldn't imagine trying to do any real work on one of these. Like it or not, W7 and all those apps you mentioned were built for a mouse - which explains why Microsoft has always been such a fan of the stylus. Up until their Zune Metro and WP7 interfaces, for me at least, I always found touch (sans stylus) on Windows and WinMob maddeningly frustrating and I don't see that changing anytime soon (maybe W8?).
Without being disagreeable, I respectfully disagree - I just don't see why anyone would want of these... it's like a touchscreen netbook sans keyboard and touchpad. For me, if I'm going keyboardless there are really just to options - Android and Apple. Microsoft would have been better adapting WP7 to this form factor IMHO.