I don’t know just what the screen is made of, but I have had an original Surface, S2. S2Pro, SPro3, SB, and now both a SB2 and SB2 15 inch, and have never seen a scratch on the screens.
I protect the device with vinyl skins to avert scratches. I also protected the SP3 screen for about a month, but removed that glass because it took away from the feel of the screen.
Use of all my devices has been heavy, including much international travel. I have used pens enough to wear down the nibs, and touch with my finger often, including tablet mode about 20 percent of the time.
The screen quality and resilience has been a bright feature of Surface devices for me.
I clean my screens about once per month with an eyeglasses lens wipe, and occasionally with a very light application of ammonia glass cleaner.
My iPhones, however always are under glass. They all seem to scratch more easily than the Surface screens. A technician once told me that the phone screen does not “give” a bit when pressed, but in contrast, the Surface has a slightly more cushioned or elastic feel when pressed, distributing pressure differently. This is likely only part of the reasons Surface screens are so resilient.