As others have said, the whole point of these machines is that they were NOT simply creative combinations of current high-end commodity products. The whole system architecture, from the CPU, memory, I/O, to the graphics hardware, was custom designed. That's something you really don't see very much of these days.
Not in PCs, but I wonder if the iPhone would count as a largely custom designed computer. They do custom silicon for a lot of the system, and get much higher performance than commodity phones as a result. Perhaps the spiritual successor to these high end workstations in an odd way.
I think Linus mentioned something along those lines: on how the work on using Linux for supercomputers was the foundation of Linux for phones. It's a point Tannenbaum makes in Modern Operating Systems: what is old, is new, and what is new is soon to be old, as the bottlenecks move, ideas that were abandoned get resurrected.
And adding to the magic, SGI machines were a something most people would never get their hands on. A maxed out graphics workstation today is still just an "ordinary PC" but more expensive. A (big) upgrade, but not something with magic dust.
