I know I'm kinda late, but I just have to say it.
Direct drives always had the potential to sound the hat off most other technologies, but because of purely economic reasons (cost!), they never actually did. Attempts were made, but they ended up being sort of half-hearted.
The main allure of direct drives was the possibility to use what is probably the best engine in this planet, namely a Hall generator motor. Its key advantage is that it is so constructed that it is, for all practical purposes, inside the magentic field all of the time. Hence, extraordinarily smooth ride, with the possibility of reducing wow and flutter to a practical zero. In addition to this, its has extraordinary torque, so it makes heavy platters easily possible, and thus ringing is all but eliminated.
Yes, it is just as you suspect by now, the problem was its construction. Manufacturing of this type of motor is considerably more expensive than of any other motor used in turntables, never a good sign. Worse, to be able to actually use the above advantages, you had to have a REALLY clean and competent power supply; and these too are rather expensive at this level.
If memory serves, Dual's 70x series used such motors, and it showed on their price tags. I am not mentioning quartz control because everybody and their dog had that, crystals clocks are cheap at that level of values and precision.
And it's not as if it appeared too late on the scene, either; Dual had its 701 model on the market by 1975 or 1976, if memory serves, so some years were left over to develop the concept. But, I think the industry never did because they were already whiffing the winds of change.
