Thanks for the link. It is very nice to see our models in this test scenery.

I saw a very similar scene in Unity3d, directly in a browser window (but I could also switch to full-screen). It displayed an entire village made with our desert models on a terrain, a lake with real-time reflections, real-time shadows and some post-processing.
I walked and jumped very smoothly in this scene, collision detection was perfect, not a single slow-down and the scene has more than 1.000.000 polygons easily.

So yes, it is also possible in Unity.

LostClimate: It is not that easy to use a real-time shadow mapping shader on a large terrain. It works only with a good multi-resolution mechanism and some optimizations. And it should take fog into consideration.