Rccc, Assuming you own high quality examples of belt-drive and direct-drive turntables, have you done the experiment of listening to each one with the same tonearm and cartridge? If so, do you hear any differences that could therefore be ascribed to one or the other turntable? What are the differences if any? If you have not done that experiment, then maybe you are premature in declaring that the inherent mechanical differences between belt-drive, dd, and idler-drive are irrelevant or inaudible.
Belt stretch
OK Im out to start an argument here. Im flattly stating that stylus drag and the effects of belt stretch on belt drive tt's is pure BS. Unless the motor was grossly underpowered there is no way there are any audible effects (even to a dog) related to belt stretching. Im not saying that there is no measureable speed fluctuation but Im saying that even if you have something sensitive enough to measure it you still cant hear it. So there