Tim, I don't think anyone would disagree w your premise that more and more accurate speed accuracy, and as you say speed stability (aka lack of drift), can only add to the illusion of reality.
However there are many ways to skin a cat. GPA have gone for DD, and v careful measurement of speed/feedback loop on a moderate weight platter. By nailing perhaps the most complex control system on speed, they've achieved an exemplary outcome.
But turn to the AS2000 or Vyger Atlantis/Indian, and you have a wholly different approach, with highly accurate motors combined with high mass/high inertia to achieve perhaps broadly similar performance, no feedback, and now advantages of air suspension and bearing. And the illusion of reality brought about differently.
Hi Spirit - i don't find there's much to disagree with in your account. I use the Monaco as an example for my views because it is the example where I have direct experiential evidence. Taking that approach does nothing to discount other's experience. I made the decision a long time ago not to give accounts of what I don't know. That doesn't rule out discussion of architectures, drive systems, topologies, etc. I'd love to hear a Vyger or AS2000 in their own right and also to gauge those experiences with what I read - but until that happens it doesn't work for me to cite such in, for example, my follow-up with Tango. Hope you understand.