Its not the raw material, its the machining and precision assembly. Holy cow, when will you people understand that?
That's an easy question to answer. The key is improved quality control.
As one who has many years of experience, having purchased something new of substance ie: computer, iPad, iPhone, year after year, I can honestly say that the quality of products I have received in the last four years has degraded quite noticeably.
Where once Apple could be trusted without a second thought, to deliver a product out of the box that looked new and functioned like new (notice I didn't say perfectly, as most cutting edge tech have some bugs), those days have been replaced by the fact that now it's a bit of a crap shoot, when ordering from Apple.
Sometimes you get properly built, inspected product, other times you don't. It's as simple as that.
I notice it a bit more than others since I work in a very large scale enterprise where we use both Apple, and Windows computers and replace them often.
Thus besides the high volume of Apple gear I buy for myself, I see a lot at work. The degradation in quality is discouraging to an Apple enthusiast as myself.