Believe it or not, just because a component comes from the same manufacturer, doesn't mean it is 100% identical to every other product that manufacturer...
Example:
The ATI video card - although ATI Makes cards for many companies, Apple has specific specifications for their cards. Most companies do - BUT - in the case of most Windows PC manufacturers, they spec out a "stock" or comodity-level product, while Apple may spec out with some specific qualities/features they want (like the proprietary video connector they use for their amazing monitors...).
Apple has been using primarily Pioneer drives, but again with a few firmware and other tweaks.
Hard Drives they do use run-of-the-mill because all that is different is the formatting, which takes seconds when the machine is assembled (Don't know if they order them pre-formatted).
Motherboards - lay any Apple Motherboard next to any "other" motherboard and find how NOT similar they are. Even with the switch to Intel processors, the motherboards are very specific to Apple, as are the power supplies.
This specification list at least partially explains the former cost differential between Apple and other PC's. But with the most expensive component of all - the actual processor, now being shared with the rest of the PC world (with only possibly minor tweaks), the price for comparable hardware has dropped significantly for Apple.
I'd never buy another pioneer drive again after a horrible experience and with 2 of them(slot loaded dvd-rom drives), also horrendous support. the hardware and component's are pretty much the same just arranged differently, are you saying that we have a conspiracy in the manufacturing where they are keeping all the good stuff for 4% of the population? :)