In terms of slogan "design," perfect grammar, and a completely accurate and non-exaggerated explanation of the product/situation often times goes out the window in preference to something that sounds better. Do you really think that when P&G advertized Crest Toothpaste with "Look, ma, no cavities!" that kids who brushed with Crest never had cavities again? Is a diamond really forever? What about multiple diamonds? I digress...
While I certainly recognize that "from their headset to yours" implies that someone is listening on a headset, well, my personal idea was to minimize the number of syllables and words to spit out. In a sense, make use of the KISS principle. In my mind, it is catchy, quick to say, and memorable. From a technical standpoint, pluralizing makes the statement sound odd in the sense that you are listening to individual transmissions from a single headset at any given time. I don't know, it just doesn't sound right, and not "clean."
Don't get me wrong, I'm not averse to change... just make it for the better. If the original slogan is not good enough for the site, then open up a new submission period for everyone! It worked well before, for a time anyway. Maybe this time let "management" select their top 3 of the choices submitted, then poll it on the forums. Winner take all.
~Nate