What is widely done and extremely misleading, is to report the accuracy of the chip used. This information is provided by the manufacturer of the chip and really has no correlation with the turntable's actual speed accuracy.Agreed. There's some correlation but it's hardly conclusive or adequate information.
It's just as inaccurate to report on the speed accuracy of the motor itself. Speed accuracy at the platter is the goal, and it's easily affected by stylus drag. Measuring or quoting specs anywhere but at the platter with the stylus in a modulated groove has little meaning.
If a turntable has a precision power supply, then speed control is addressed by default.I disagree. A precise source of power is certainly essential, but it isn't sufficient. Power must be converted from electrical to mechanical energy by the motor, wherein many opportunities for inaccuracy reside. Even if the motor does that job perfectly (and no motor does) that mechanical energy must be transmitted to the platter without loss or inaccuracy, another opportunity for errors. Finally, the entire system must be able to overcome the variable load of stylus drag whilst playing real records, an extremely difficult engineering problem.
I agree it's vital, but maintaining constant and accurate platter speed under variable load is a terribly complex problem, and no set of wow and flutter measurements will come anywhere close to identifying how good a particular rig really is in this respect.