Well, this topic always brings up contrasting opinions, it was just a question of time
I have to agree, that coupling the speakers to the floor adds building vibrations at some degree. If you have a floating parquet flooring, that will be quiet audible. But if you have a glued down parquet flooring or concrete floor that is totally negligible.
By the way; most building vibrations are caused indirectly by the air vibrations anyway, not the speakers coupling the floor itself.
Decoupling a speaker from the floor only helps little to reduce unwanted noise annoying your neighbours etc., it´s simply a myth. In theory it reduces noise a bit, but most vibrations are induced by the air sound pressure anyway. Decoupling works for a washer, but not really for a speaker...
Coupling the speakers to a (hard) floor is a big advantage for transient response, I´m actually a little shocked you are denying that. The justification is actually very simple, the speakers gain restoring forces by coupling to big masses. The same is true for a massive enclosure...
Decoupling a disc player is a totally different story. This really does make sense to me.