I reckon it's all down to good/bad luck. I've no case or screen protector for mine, and I've dropped it (on wooden floors) several times, even had it in my pocket with keys & coins on occasion, and no scratch on the front or cracks on the back.
As for screen protectors, I'd never use one. I'd rather have a scratched screen (& thus, a new iPhone) say, once a year; rather than an ugly screen protector or case 365 days a year.
As for screen protectors, I'd never use one. I'd rather have a scratched screen (& thus, a new iPhone) say, once a year; rather than an ugly screen protector or case 365 days a year.