Pardon if I missed this but setting aside bands, it seems that the only differences touted between the Sport and Watch are the watch face material and case material. On the back of the watches they also identify Composite vs Ceramic back, respectively. So what's the deal on that? The case looks solid, I guess they are referring to the backing in which the sensors are set. Hard to tell from the photos, but it looks as though that material is bare and will be in direct contact with your skin, no? Just seems weird, that strikes me a sizable difference to not hear much of anything about it.