Very good point. Even if you eliminate the suspension/lack thereof and drive mode (w/ or w/o bel)t, DC motors sound quite different from AC synchronous motors in the same table. The hunt and seek of a DC servo motor does wreak havoc on the music coming off the table, IMHO. Various designs have thrown gobs of platter mass at the problem of speed constancy, but that introduces the problem of energy storage and later release (mechanical capacitance, if you will), which smears and obliterates detail and timing.Even staying within a particular design brief, interesting things can happen. This past CES Audio Note started the show with the long-standing TT Three Ref, a three motor suspended belt drive table with external power supply, until the prototype of their new redesign arrived, (also 3 motor, external supply, suspension, new chassis and who knows what else.)
Swapping the same arm/cart combo from table to table in an otherwised untouched system, my reaction to a Nirvana LP reversed 180 degrees from before (old table): "Jeez, I'm really not in the mood for this now!" to after (new table): Jumpin' around the room playing air guitar! (Anyone who knows me realizes how unlikley the latter response is!) I have no explanation, but the latter combo simply set my head on fire and insisted that I "get with it!"
Nota Bene: Clearly, these days I have a commericial axe to grind in this area, but I gathered my initial impressions and reached all these conclusions a long, long time ago, and have found nothing to cause me to change my mind yet.