It has been known for some time now that apple outsources all their parts manufacturing to various foreign companies. It's a money saving strategy, that is part of Microsofts business model with the xbox 360. The whole point of outsourcing is to get the same component at the lowest price. The overall effect is that all apple products contain parts from many manufacturers. This is constantly a problem in companies that do this, since maintaining quality control on parts from so many places is not only difficult, but next to impossible.
Take Microsoft and Sony as examples in the home video game console industry. Microsoft outsources everything, which has resulted in an XBox 360 failure rate of close to 30% (this report is available all over the net, just do a search if your interested). Sony on the other hand, manufactures all of its PS3 Hardware in-house. The result? A PS3 failure rate that is actually less than 1%. Now this isn't specific to sony, the same is true for Nintendo, who also manufactures its hardware with in-house components.
The point is, the obvious quality control problems that apple has had in recent history (it wasn't always this way) is due to this business model. And the fact is, they don't intentionally put sub par parts into their devices to save money, they just can't possibly keep track of every component in a device that may literally use dozens of different manufacturers to make.
So how do they deal with this, since they certainly anticipate problems. Well, they have the best damn support in the industry. They balance their manufacturing risks with good support to their consumers, and the overall net effect is that it is worth it, and they make more money by outsourcing. Eventually, if there are enough customers complaining about a particular component, they phase it out. Which is what happened to the lcd screen used in the last rev 15" powerbook (anyone remember the "horizontal line issue"). Well that screen no longer exists, and anyone who gets a screen replacement now will receive one without the lines. Unfortunately, this is just how apple does business. But like I said before, it's not exactly an uncommon strategy.