It's not just about the listening room. It's the opposite, the more you reduce what your room is adding to the equation the more you will hear the room in the recording and how the speaker images that stereo information.
If a specific pair of speakers are properly setup in a fairly good listening room, a room that is not masking the sound too much and give you a better ratio of the direct sound from the speakers, you will hear how they render the stereo field different than other speakers, and that same characteristic will follow them from a room to another.
The characteristics of the speakers will often differ, some speakers have a more forward "in your face" kind of sound while others sound more laid back, and some speakers can image a wider sound field while another is giving you a more focused sound and sometimes better layering and depth.
I have nothing against using one single speaker for quantifying distortion and frequency responses, but there is so much more to the characteristics of a pair of speakers that can only be heard by listening to them in stereo.
It's not nonsense, it's a big part of how a specific pair of speakers reproduce the information that's on the recordings, and it can be "everything" for a listener and the deciding factor why the person chooses that specific pair of speakers over another.