In all honesty; I was as surprised as your are. 
I always assumed that hardware gear would be much more stable and that software would be much more jittery. You can still see my surprise on the first page of that thread when I first test my MPC 1000 back in April 2015 just after finishing building the testing device…
Yes, I am aware of that page. I’ve just been testing MIDI Clock output while these people also seem to test the internal clock stability. However, they don’t publish their procedure or any way to verify their results independently so I’ve always taken their results with a big grain of salt.