The little things add up. A few pixels here, a broken alignment there, they make the overall design look unkempt. If it's egregious enough it makes things look sloppy. It may not seem like a big deal, but getting things pixel-precise makes someone a better, more fastidious designer.
but look at the iphone button example. Can you see the difference between the good and the bad? I can't. even side by side, they look identical. the same with the 'blurry button' example.
Now, maybe you are right, and maybe most people can notice those sorts of things... I'm just pointing out that I can't.
