Hood,
Arguments are emotional and useless. Debates are factual and beneficial. Methinks we are both fact guys. You are far more experienced than I on these topics and I certainly would not question your observations. What it means to me is that both behaviors occur, and that becomes the fact that begs explanation.
You mention following error on a lathe at 45k. Three significant differences in my scenario (and I perhaps that of the OP) steppers, three axis moving simultaneously, high speed. Which actually brings up an interesting point; In the past, I had all steppers and therefor had no point of reference outside that realm. However, with my current odd combination of steppers and a servo on the same machine, only the stepper, which was maxed out speed wise in the motor tuning, lost position. The servo was spot on, although it was nowhere near maxed.
I make the assumption that Mach sends only pulses and no positional information, therefor it must have sent all of the pulses to the servo in order for it to maintain its positioning. One interpretation of this would be that these curious errors are confined to steppers. I have observed the lost steps with three different models of stepper motors on two different computers. All were being driven by Gecko203V, so perhaps that might be a suspect.
An interesting twist on this topic is that the Smooth Stepper in invariably described as having a 'high quality' pulse train. The logical implication being that Mach and the PP do not produce same. Although I do not recall ever reading any hard evidence to that effect, experienced an knowledgeable people use the SS, so I have to assign credibility to the concept. Taken together, all of the above evidence might seem to siggest that the Gecko 203V is particularly sensitive to a 'dirty' pulse stream, yet the OP is using differnet hardware, which defeats that theory. It takes time to learn which sources are reliable and which are not. The lesson in all of this is that in a situation where an unresolved problem is manefest, all possible known causes deserve mention.