What doesn't slide is that supercomputers cost more.
Here's a simple test.
Suppose that I give you these two measurements:
SPECmark: 1.2 million.
SPECmark: 3 million.
Which one is the supercomputer? Without knowing the date, there's simply no way for you to tell.
Suppose instead I write:
System cost: $20 million 1990 dollars
System cost: $400 1990 dollars
Which one is the supercomputer? I think most people will be able to pick which one is which.