Emilio, I don't know who you are talking about when you refer to "highly skilled professional machinists", nor do I care to know. But the laws of mechanics and physics are generally reliable. There is spring tension from the indicator, as well as mass and gravity at play here. And, there is really no such thing as a perfectly rigid support. Years ago at a World's Fair, I can't recall which one, GM put a extremely sensitive indicator on a steel plate several inches thick and invited people to press down on the plate. Most were surprised that even hand pressure was enough to deflect the bar. All these factors combined add up to what Richard is demonstrating. I would grant that the exact setup that Richard used could have been chosen for its susceptibility to this phenomenon, but the facts are that what he showed is true. It was only a demonstration. Proper choice of materials, etc, can mitigate the effects shown, but not totally eliminate them. Whether it is acceptable or not depends on the accuracy need in any particular situation.
And BTW, we have a number of highly skilled professional machinists here as well.