I saw mention of it on another forum by another poster that claimed they'd contacted Apple Support about it and the Apple Support rep admitted it - I can add no credence to that, I'm just offering what I read earlier that someone else posted (their experience).
If it's true, and there should be a coating, I can understand that to some degree but, as a licensed Ham operator for over 3 decades now, the entire concept of putting any antenna in range of actual skin contact (even in spite of said "coating") is just idiotic engineering, any way Apple or anyone else cares to try and slice it.
It just won't work, and I honestly can't believe that Apple went in this direction... I questioned this idea when the first prototype images were leaked out months ago and now I can see that my original line of thought - that they might use the band as some type of antenna or coupling - simply wasn't going to work. Now, months later, my hunch seems to have turned out to be true.
Again, they should have just put the antennas behind the glass backing... or even better would have been to embed it inside the glass, like the types of antennas that cars have for their FM radios, it's embedded as thin wires inside the actual glass itself. That would have been infinitely superior to what they've done, based on my knowledge of antennas and radio wave propagation.
Bleh... this will just get worse as time goes by.