As Sean said above, any variation of a DD motor is tranmitted to the platter. That's the big rub: speed changes. Most DD motors are constantly increasing and slowing their speed to adhere to the desired speed setting. These speed changes may be minor as a percantage increase or decrease of overall speed, however, even a miniscule change will affect pitch.
And perfect pitch is what it's all about, eh?
And perfect pitch is what it's all about, eh?