I think the reality is that your phone will always encounter something that can damage it (unless it's made out of diamond), and a case lets you easily replace the damaged part.

Just subjectively, I remember having a super scratched iPod and it just felt kind of ratty every time you looked at it. Meanwhile, a phone in a leather case gets kind of a patina that improves with age. It is kind of sad though, I got a really pretty blue iPhone and you wouldn't even know it because it's completely covered by a case.

I'd rather see phones that aren't perfectly flat but instead have proper built-in mounting things. Give me some screw holes to attach a set of 4 bumpers to the corners, and a camera mount thread hole in the bottom.