@terry9 Like with many quantities, the speed aspects of turntable rpm can be described as a mean surrounded by skirts on either side. I say this with trepidation, because the turntable noise is not a stochastic (random) phenomenon. It can have resonances, for example. However, narrowing the width of the frequency spread and diminishing the signal from resonant sources is a worthy goal.
Some say that a turntable that has poor rpm control cannot bring out all the nuance that a high end cartridge can pick up from an LP. This reason alone is why some people are interested in the stability of the RPM. The human ear is not a good instrument to evaluate rpm. One may prefer one or an other method of rpm control because the sound of one is more pleasing than the other. Comparisons based solely on listening is obviously important. This type of comparison is not quantifiable by nature. Specs are there to provide a guide to potential users.
Engineers develop a product based on numerical specifications that the company's sales and marketing generates. Engineers use test instrumentation to measure and compare design approaches. Without a formal methodology and explicit specifications, engineers do not know what nor how to build a product. And importantly, when to stop engineering and consider the problem solved.
Measuring performance parameters of instruments is crucial to product development.
Any company that does not report these values via a spec sheet is denying the customer one way to evaluate and compare different instruments. Some customers need to see these specs because they provide a baseline for the performance of the instrument.
Not publishing a spec prevents that from happening. Often known code words or phrases are used to appeal to the emotions of particular enthusiasts. These are not specs. Perhaps some don't care. I do.