[sdiy] dirty/clean ground again

[Roman]

Hi,

I had an idea when I woke up this morning. Most of module circuit are made
around opamp, right? Let's simplify and not use any transistors, or logic ICs
for a moment. So now, signal path is like this:
power rails, opamp output transistors, output resistor, patchcord, next module
input resistor, or pot,
opamp summing node, feedback resistor, opamp's output, power rails.
During this route there was not a single contact with ground (unless we use pot,
but I'll leave it for later),
so basically current in ground pin of entire module should be 0. So why do we
all decouple opamps with dual caps to ground. Isn't it more justified to use
single cap just across power rails? The current spikes are there only, leaving
ground as reference voltage. With CMRR and PSRR high enough it should have no
impact on signal even if power rails travels with respect to ground in
semi-uncontrolled manner.

Am I missing something?

Right, when we use pot, part of the signal (thru 100k ussually) goes to ground.
But even with multiple inputs it is in microamps range. Am I completely nuts
here?

Roman