I've read that the sapphire Apple uses isn't as scratch resistant as other watch makers' sapphire - whether that's true or not, I don't know. All I' have to go on is my own experience, based on 2.5 years of wearing an S0 every day and 9 months of wearing an S3 every day. The S0 was absolutely PERFECT when I sold it, but the S3 has three very tiny but very deep scratches. My usage patterns have not changed, in fact I've put the S3 through a lot less than the S0 (I took the S0 snorkeling in the Pacific several times, which included time on the beach - with sand, obviously - not the best place to be wearing a watch) ...
I'm not accusing Apple of anything (and I'm waiting on my S4 SS to be delivered!) - I'm just saying that in my experience, the S3's sapphire has been far less durable than the S0's was.