You raise an interesting question. I would think they just scale the app, especially since the elements in Modern apps are pretty big to be touch friendly.
But, they aren't forcing a 1024x768 requirement, thats the bare minimum. of course, technically Toshiba did some 1024x600 scaling magic, but let us not speak of that display.
And what do you mean with alienating machines like that? With Windows 8.0, they annoyed me with the 1366x768 (?) requirement for snap while my laptop was 1280x800. At least they relaxed the requirement in 8.1, which made me happy.