I don't know if I've just been excessively lucky, but I've never put a case on any smartphone I've owned since 2010, and I've only cracked the screen on two of them. These days (probably for the past 4 years) I do put the thin-film screen protectors on as well, and replace them if they get damaged.
I've always been of the feeling that I'm buying this lovely, well-designed piece of hardware, why would I want to cover it up in an ugly plastic case?