just like DOS, Windows 9X, Windows 2000, Windows NT4.....
you don't see any of those nowadays except very rarely you may come across an old Win2K server that someone's forgotten about
I agree with the general thrust, but the rate of shrivelling is slower than you might imagine.
I have come across 3 NT4 installations in the last couple of years. And as for Win2K, well there's a surprisingly large amount still out there, believe me.
The sad thing is that some projects are going on right now to upgrade 2000 to 2003, because of the incompatibility of the applications with Server 2008.
SD