Just to be accurate there are multiple vectors for mains noise signal corruption. This symmetrical power while IMO impractical (for safety/compatibility reasons), really does have a scientific basis for potentially reducing some types of noise. Instead of 120V signals all around, the dual 60v is 1/2 the peak voltage to begin with. The outside world is not looking at the two mains leads differentially. To the outside world it does look like less voltage. In theory this means less noise picked up by nearby signal conductors. Besides 6 dB smaller mains voltage waveforms the two symmetrical waveforms will possibly cancel out. Visualize one leg pushing noise while the opposite leg is pulling an exactly opposite version of that noise.
6dB+ less noise is not inconsequential if hum is the dominant noise in your studio, while good practice using well shielded (balanced) wiring will generally make hum a non-issue (with modern well designed gear).
So IMO not a pure marketing invention. More like a well intentioned, if not slightly desperate, attempt to deliver a quieter working environment in simpler times.
JR
PS: WRT isolation transformers, all transformers are bandpass filters so very HF noise on mains can get filtered out by an isolation transformer. FWIW the products normal transformer will act like a filter too.