Matt Richman crunches the numbers:
Apple makes more money from the sale of one Mac than HP does from selling seven PCs.
Andrew Richardson goes even further:
If the average selling price of a Mac runs about $710 more than a PC (ASP of a Mac - ASP of an HP machine), and about $320 of that is profit, then the remaining $390 must be those higher costs. Apple’s computing hardware, and the software development behind OS X, actually cost more to manufacture. Given the volume their manufacturing partners are turning out and the squeeze to contain costs put on them by Apple, one has to wonder why.
The answer is fairly obvious to anyone coming to Macs after years of using commodity PC equipment: better design and build quality costs more.