Funny that this comes up because I recently dunked an older, 90's navy bag and it had a whitish sheen to it...almost not noticeable and very even. The bag itself was very clean but I wondered if the whitish stuff was some sort of conditioner that has been applied.
Whatever it was came off easily with a bath. I doubt the silicones REALLY hurt the bag, but they probably don't help much, just make it shiny in the short run.
Since the conditioners and cleaners are likely just some product they contract out, it's too bad they don't go with a company like Apple or Leather CPR that would probably HAPPILY put the "Coach" name on their product in order to get that revenue rolling in.
Can you tell I'm a business major?

YOu're right, I bet the "sheen" is very like a built up residue such as a silicone based substance. It probably doesn't hurt it, but the newer bags with cloth linings that can't as easily be dunked would be harder to clean that stuff back out of!