Apple designs a product knowing it will sell millions of copies, so it makes sense for them to spend the time to get it right. PC manufacturers have greater volume, but no individual product is anywhere near as ubiquitous as a Macbook Pro or iMac. They're stuck in a trap where no single model can sell well enough to justify an Apple level of quality even if they had the design sense to produce one.
Close, but Apple's real secret is that they make premium products, with profit margins that allow them to invest in researching the next big thing and spend time doing it right.
Dell, HP, Sony, Acer, Toshiba, Lenovo: these guys live and die by razor-thin margins of the "we'll make up for it in volume" strategy.
Ultimately I think a (un)healthy share if consumers just don't care about the details of the experience enough to spend more money.
