I totally get this. Unfortunately for the OCD riddled amongst us absolute SQ occasionally runs askance of the best intentions of those that would protect us.
Liberty!
But, how does safety ruin SQ?
Grounded chassis need not even be in the circuit.
Indeed. However, most pieces of audio gear are not double insulated and therefore removed from the AC ground.. Problem is that almost gear has a ground reference that is connected to electrical ground. This connection is then connected to the power supply and then referenced to the power supply ground plane and then raises all kinds of hell with analog and digital grounds.
Analog ground plane noise is relatively easy to address, but most manufacturers are oblivious to thus in the consumer audio realm. Oddly enough many of the high end builders overlook this noise source and expect a very stiff power supply to take care of the noise through common mode suppression done by filters in the PS. Sometimes this works. Often it does not because the bean counters don't want to spend the extra $$$ to take care of it.
Differential noise is different animal and requires a lot more to treat it.
Noise of all types suck. It moves us just that much more from the playback and reality.