J: While i don't know how common it is in audio gear, some RF designs make use of two different "grounds". One is a board ground and the other is a chassis ground. In some instances, it is beneficial to have these two grounds separated and in some instances, it works better to have them tied together. I don't know if this is what Plinius is doing with their switch, but it might explain some things.
Personally, i've always wondered why audio components tied circuit ground to chassis ground ??? If audio engineers were "smart" ( some really are, some ... ), they would use the chassis as a "Faraday cage". In effect, the chassis would be tied to electrical ground but NOT to circuit ground. This would increase the rejection of RFI and minimize the potential for damage via inducing stray voltage ( static shocks ) into the circuitry. While this would mean that all of the external signal connections ( RCA's, XLR jacks, etc.. ) would have to be isolated from the chassis electrically, that is not really a big deal. It might raise the cost of a product slightly, but hell, we're already paying too much as it is yet we come back for more with every purchase. Sean