Many of these problems are likely design issues, not manufacturing defects.
Stuff like cracked casing, top cases that turn color...these seem like design issues due to choice of material and thickness of the top casing (though its impossible to say for sure.)
This happens a lot with first gen Apple products because their designs almost always push new trends and are not based on previous designs (for example the magnetic latch of the MacBook, and how the screen rests against the top case with the raised ridges.)
I'm not defending the defects, but it is easier for say Acer or Dell to swap some colors or slightly change the shape for a new notebook model and call it a day.
Apple also makes a lot of design choices for aesthetic reasons, which are great if you don't have a problem come up. For example, I really like their notebook power adapters, but many people have had problems with the strength of the thin cord (mainly where it connects to the adapter.)
It is what it is. The problem rate is low enough for me to continue to choose Apple products (and I had to bring my MacBook in for the cracked case problem), but that's easier for me to say since I've never had out-of-warranty issues. Another choice is to simply never buy a first rev. Apple product, not a totally unwise choice since you have plenty of options to choose from, now that the Intel transition is a couple of gens old.