Why SL + XNA? Because this is what is being used to create WP7 apps, the exact type of apps that people want on a tablet. Creating desktop apps to run on a tablet is just not what people want. In addition, if developers can easily target both WP7 as well
as the tablet UI with the same code, it would mean that there will be a lot of apps on the tablet that work well on that form factor.
I see your point about the hardware issue but this is something that can be addressed in the future. BTW, are you saying there will be
no tablets running Windows 7? Because they will run into the same issues you mention, right?
They'll exist, sure; but you won't see any of them becoming fashion icons or in any way become "desireable". Microsoft would be better served by supporting the netbook movement., at least that has a physical keyboard and x86 compatibility.