My daily driver is a Citizen Eco-Drive Titanium. The metal itself is obviously utterly unmarked but the screen is heavily scratched.
I've been wearing a watch daily ever since I was a child nearly forty years ago and all the rest of my expensive watches (Breitling, TAG, Omega and Rolex) are in perfect condition as they are used much less frequently and never in circumstances that my daily watch is subjected to. The Apple Watch I see is more of a replacement for my daily driver so I expect it to get pretty beaten up especially as even the stainless steel variant will be more prone to damage than my current daily watch. Because of this, I want to take care of it, hence a screen protector and maybe a case, to ensure the longevity of the device.
*shrug* Horses for courses.