I didn't use a screen protector of the Galaxy S9, and yet it didn't suffer any scratches. Any blemish you see on the screen is dust, or a reflection of the sun.
The Galaxy S9's display uses Gorilla Glass 5, which is tough and scratch-resistant glass. Gorilla Glass 5 is also used in other high-end smartphones from Google, LG, HTC, and even less expensive phones from OnePlus. With that in mind, you could say that other phones with Gorilla Glass 5 would escape the car treatment without a scratch. But I wasn't willing to place more phones under my car's tires to test the theory.
Apple's latest iPhones – including the iPhone 8 and iPhone X – could also potentially fare just as well as the Galaxy S9, if not better. According to 9to5Mac, Apple worked with Gorilla Glass to make its own tough glass that's even tougher than Gorilla Glass 5.