I agree. So are speakers. Can't you hear differences through them. Can't you converse in a crowded room or near a waterfall?
You speak of speaker or room masking as if it were this big blanket blob. There are so many types of distortion.
Your analogies are completely off. Single tone decay caused by room will mask single tone decay caused by cabinet resonance.
Harmonics generated by distortion of the single tone played by speaker will mask the same harmonics generated by electronics. Same will happen if you measure IMD, which is the same thing but some more harmonis are generated in that scenario.
No offense, but i think you should read some basic stuff first before posting so much here.