I think farbrausch's earlier 64k-efforts are better, despite their limitations from the underlying DirectX API.
Short of talking directly to an NVidia card, which of course would likely make this demo only compatible on said hardware, Direct3D is the closest you'll get to the hardware. It has one less layer then OpenGL (OpenGL being a state machine) and at this point, especially with Direct3D 10 now, it has more whizbang features.
All that being said, you could certainly write such a demo in OpenGL, but Direct3D is a fine API.
