Comment by WillAdams

Call it the X-Windows factor --- software gets more capable/more complex and there's a constant leap-frogging (new hardware release, stuff runs faster, software is written to take advantage of new hardware, things run more slowly, software is optimized, things run more quickly).

The most striking example of this was Mac OS X Public Beta --- which made my 400MHz PowerPC G3 run at about the same speed as my 25 MHz NeXT Cube running the quite similar OPENSTEP 4.2 (just OS X added Java and Carbon and so forth) --- but each iteration got quicker until by 10.6.8, it was about perfect.