Win98's faster shutdown is a restart of the 32-bit kernal without having to restart the 16-bit DOS kernal sitting underneath.
Since Win2K is fully 32-bit and not sitting on top of DOS, there is no 32-bit portion to restart, and no 16-bit portion to keep in memory. That's why you cannot do a fast restart of Win2K. The closest thing that you can do is log off, and then log back on.