I'm pretty sure Microsoft hasn't forgotten that. It's subtle in the video, but the applications are more than in just one "virtual screen" spot and seem to remember where they were left (Outlook and Edge are in very different positions in her space, for instance). Same with the virtual knick knacks and doodads scattered in the space.

The promises from earlier Windows Holographic pitches is that it is very space-aware including making it easy for multiple machines and people to share a consistent space between them.

Certainly there's probably a lot more that the 2D applications could make use of 3D space, but the point of the demo (and Windows Holographic) is that existing 2D applications play nice in your 3D spaces.