The problem with your argument is that noticeable scratches on a car are large. A broken radio is a malfunction. A stall on start too. Lemon laws are in place to cover some of these.
But imagine looking for scratches on a car that are the size of scratches people are finding on the iPhone. I guarantee you there are tiny iPhone sized scratches *somewhere* on nearly every brand new car...wiggly buttons here or there...maybe a tiny bit of misalignment in the trim...a piece of untucked carpet...etc.
People are scrutinzing a $900 phone with FAR more intensity than their $30,000 cars. Why? Maybe it's the size. It's easier to find defects on a smaller object. Maybe it gives them a sense of control.
The equivalent defects that you mentioned on a car, for an iPhone, would be a gash in the case, a non working speaker, or one that won't boot without 2 restarts. THOSE are genuine defects. Micro nicks are not. I'm not saying they're not annoying, or even exchange worthy. Maybe they are. I'm just saying that comparing them to equivalent imperfections on a car is silly.