I think that in the '70s the Technics DD turntables posed a threat to the emerging high end status quo. High end brands of the time represented USA and European efforts to beat back the onslaught of mass market audio from (primarily) Japan. When Ivor Tiefenbrun made his tours with his Linn turntables, he was discrediting the DD principle in favor of cottage industry belt drive turntables. To me, however, it was sleight of hand. The comparison tests created the widespread (and persistent to this day) conception that the DD principle was inherently flawed. What was not apparent is that the Linn suspended turntable was what was draining most of the noise. While the belt drive drained some of it, it also introduced speed fluctuation as the belt flops and wobbles. That's why these days people try to replace the stretchy belts with dental floss or mylar tape, and VPI finally came out with a rim drive.
01-29-12: Tonywinsc
It is clear that the Technics tt is best in class for speed control. And that should be an indictment for all of the high end hifi turntable makers out there that seem to come in at a distant second for speed control with motors and/or drive systems at 5 or even 10 times the cost. But while we can give kudos' to the Technics engineers for their motor design, they failed to follow up on optimizing the other design parameters of a turntable. It is a valid question to ask: Why can't someone build a commercially viable turntable with a drive system like the Technics, but with the isolation and support structure for a decent tonearm that doesn't cost upwards of $12k?
This created the high end dogma that BD=Good and DD=Bad. Truth is, the Technics DDs had it all over the cottage industry BD TTs regarding speed accuracy and inherent noise floor. What was not apparent is that the Linn had *other* features that drained vibrations and controlled resonances that the popular-priced DD tables didn't do well. If--rather than vilifying DD as a concept--the UK turntables had bought the Matsushita-sourced DD motors in bulk and then sued their engineering to drain vibration and control resonances, then the TT industry would have produced what you envision here--an affordable table with low noise floor and speed accuracy.
You don't get the speed accuracy of a Technics SL12x0 'table on any belt drive table under $5500
Why Technics didn't continue to develop the table after 1981 is a matter of business model. The units became so affordable ($399 from Musicians Friend for awhile) because Technics had ceased any significant further development. After 1981 they knew they had to shift to CD and digital audio. The Technics turntables stayed in production for as long as they did because the bigger turntable market shifted from quality home audio to DJ use. If it hadn't been for that, Technics would have discontinued their DD turntables when everyone else (Denon, JVC, etc.) had. There was no motivation to improve it further except for DJ use.