I can understand your frustration, but you can't claim that Apple's QC has decreased.
In the last 4 years either myself or someone in my immediate family have purchased almost every generation of iMac and MacBook. In addition to that, I own every full size iPod since the 4G Mono, together with an iPod Mini and now the iPod touch.
This isn't to brag, but rather to state that I have not had a single problem with any of these products other than my current iMac which suffered from a graphics problem. It was replaced by Apple and I was given £100 credit.
In addition, Leopard has been flawless for me and runs as great as any of my machines with Tiger (although they run great too).
Therefore, I 100% disagree that Apple have either lost sight of their Macintosh business, the Mac OS X business or that they have a problem with their QC.