What you say is right in principle, though. Microphone cables and turntable cables carry voltages much smaller than any of our other equipment.
You can find these arguments even on Gearslutz. One guy says he can hear an appreciable difference, another offers to analyse and compare the recordings, and finds no difference. So even studio guys do not always agree on this stuff. There are more electrical engineers there, which sometimes makes the conversations even more polarized, but also leads to a lot of good information. And that doesn't mean that all the EEs are always on the same side either!