Yep it is pretty obvious when you listen to it that they are doing something and my guess it has to do with timing or more precisely, timing tolerances. I say this based upon my experience back in my early TT days (early mid 70s). I never could find a TT that sounded right to me until I listened to a DD table. Turns out I was and am hypersensitive to speed variations and it was subtly annoying me. I could be ( and probably am totally) wrong but that's my story and I'm sticking to it.
Oh and it doesn't bother me that they are being obscure about exactly what they are doing because, as you said, if they told us, then anyone else could also do it.