I also wonder what machine he is getting this FPS on.  Furthermore, Silverlight does have some multithreading capabilities that I could see being used to speed up the rendering really well.

Maybe also he is using an optimized data structure.  For example, Analysis Services 2008 is using the probability based bloom structures for sets with NULL/Empty records.  Just by moving to this structure cubes with sparse data performa 20-30% faster. 

I wonder if something like that is going on where if it is doing simple png rendering with buffered rendering on other threads with some advanced probability data structures to figure out movement.