A luxury handbag is a cosmetic item, so cosmetic imperfections are taking away from one of its primary functions. Replacing it because of a cosmetic issue is normal, because you bought it to look good. Replacing a functional hiker's backpack, on the other hand, because of a slight discoloration - is a different case, even if it's expensive.
A premium notebook is, while usually attractive, not a cosmetic item. I love how my Apple devices look, but small cosmetic issues are not as important, because their primary function is not to look good. Again, there is a balance here - some cosmetic issues warrant a replacement, in my opinion, because you do want to get a quality product. But returning a MBP because of, say, light leaking from the keyboard - that's not worth the time and effort. Especially since the results might be worse.