Often comes down to luck. Or just the way something might strike the watch that one time.
So while plenty of examples from users never having issues with the glass, there seem to be more who experienced the opposite. There are quite a few who report issues with the sapphire too.
Sapphire is harder than glass, so less likely to scratch. But it can scratch. Maybe the first time you wear it, and never again. Or the day you go to trade it in or sell it, after you've owned it 2 years w/o issue.
More likely to show wear on either version is the external glare coating.
Unfortunately, Apple is forcing customers to get the cellular version if they want SS and sapphire. An ALU cellular is $100 more than the GPS ALU; sapphire and SS adds another $230. While you can't compare the tech cost in the AW display with sapphire to a traditional watch cost, it's impossible to get the feeling Apple is screwing it's customers here.
On a traditional watch, even a gas diver, which has the thickest sapphire, a new sapphire crystal can cost as little a $30 retail as a part (not installed). The amount of SS in a traditional mens watch, w/o bracelet, is at least several factors the amount of SS in an AW. I'd be fall-on-the-floor stunned if the total upgrade to SS and sapphire on an AW costs anywhere near $100 including all the SG&A applied.
It sounds like this Apple heavy handed, "take it or take", "because I can" mind set is leaving many customers with a bad taste, a feeling of being taken advantage of, on the AW SS. As long as we keep buying, the will keep doing that. Eventually they will not be able to: China has all Apples's tech, all the mfg capacity, so could start making identical clones tomorrow. And the Samsung is right on their heels.
I bought the SS version for the reduced probability for scratches. But it's not scratch proof, so I will treat it like my mechanicals: with care.