Noise cancellation 101. Typically, any audio transmitted over the speakers is subtracted from the input the microphone picks up. It's not perfect because the shape and contents of the room distort the sound coming from the speakers by the time the mic picks it up. But it's better than the alternative of just leaving the noise in there. All video and voice conferencing apps and devices do this. Your phone does it too if you're using it in speakerphone mode.
"Furthermore, Nuance Communications is a far cry from the NSA or advertisers."
If the data is there, it is accessible by the NSA. That is why people have a concern about this. Listening to Samsung say "oh we have decided to only share it with X person, so you're good" isn't making anyone feel better. Having the information in the first place is what is alarming to people, not what Samsung is CURRENTLY doing with it.