Direct Drive turntables

I think many DDs, even in the early 1980s when TTs were at their volume peak and technology development costs could be spread over a large number of units, were hampered by less-than-ideal implementation of plinth/isolation features. Because BDs usually have an outboard belt, and a smaller motor which vibrates the platter bearing less (ceteris paribus), it is easier/cheaper to make a BD TT with acceptably low self-generated noise issues than it is to do the same with DD TTs. It was that way in the golden age and it is that way now. Also, a big high-torque but very quiet/smooth direct drive motor is a very expensive thing to make these days. If one can defeat motor speed stability issues on a BD through the combination of belt/pulley slippage being overcome by supremely mass-y platters, it is easier and less expensive to do a BD TT.

At the top of the heap of the best BDs and the best DDs, among all the tables and technology implementations I have heard, I find isolation and platter weight to be far more important than most people give credit for.

As it is, the best DDs from the past can easily compete with BDs of now for similar money (I would say they generally beat tables of now if one is willing to put the same amount of money into it). That said, you buy used, spare parts are limited, and there is rarely any significant manufacturer support (I have had Exclusive and Denon tables repaired by mfr-sponsored repair subsidiaries. I know Sony will. I know Kenwood won't, and lots of Pioneer, Sanyo/Otto, Technics, Sansui, Hitachi, etc owners are plain out of luck.

What Lew said.

Raul,
Absolutes are difficult to support in any case.
As you realize, doing a controlled-environment test where everything else (platter and materials, bearing, isolation/suspension, plinth, arm, cart) are the same is quite difficult. I can imagine a technical construct where one could do so, but I have been ridiculed on these pages before for asking about it :^) so even a well-implemented solution would obviously have its detractors. So we are left with the opinions of people who spend a great deal of time and effort trying to "get it right" and each one provides their own opinion based on their own experiences - there are few people who have spent any serious time listening to cutting-edge implementations who would disagree that it comes down to the whole of the implementation rather than a single piece of it. While arms/carts can be moved around from table to table relatively easily so as to provide a 'constant' reference, set-up is yet another issue to deal with. So it obviously comes down to a "in my opinion, in my system" kind of opinion, and it seems that is the spirit in which the posts have been made to answer the OP's questions.

Mike, Raul,
Actually, the 0.001% Raul quoted is equal to 10 parts per million (it already has the percent sign there). Lots of Japanese DD tables had a 10-20 parts per million speed accuracy spec (at least using the most advantageous measuring method), but those tables which also had a quote for speed drift limitations generally allowed a lot more speed drift than that. I expect that the Rockport, along with the P3 Shane has, and some of the other expensive motor tables, limited allowable drift to about that level as well, and then used a variety of methods to reduce the speed/violence at which deviations were brought back to normal (i.e. platter mass, a drag function, torque attenuation (P3 has a torque attenuator circuit), etc).

Phil, I agree that the inflation calculator does not answer the question. The channel inefficiency part is key. Another point was that in 1978, the USD/JPY rate was much higher than it was today (the dollar was at twice as strong vs the yen, and for a decent part of the year was 2.5x stronger). Indeed the USD was much stronger against a host of currencies. Most of such a table would be manufactured outside the US I imagine and would therefore have those local manfacturing/profit margins built into non-USD currencies before being brought here to have another multiple (or two) taken on the sale.