Sorry I wasn't trying to imply they were completely different, and Honda in particular shares a lot of parts between their two tiers, but this mainly happens at the bottom of the "luxury" line and the top of the "regular". While I agree that there is probably a bit of the price that goes into the badge, I doubt it is really a large amount, and luxury dealer networks definitely cost more to operate than "peon" brands. You are suggesting that Nissan, Honda, and Toyota are all colluding to artificially to take huge profit margins just by slapping a badge on a car? While that is happening these 3 luxo marques are facing stiffer competition across the board from the Korean brands, GM, Ford, European, heck even cannibalizing their own sales with their "peon" brand (why buy an ES300 when an Avalon is almost as good).
The intricacies of car manufacturing and sales is much more complex than computers, which is why I believe it to be a bad analogy.
Even in your post above you try to strengthen it by saying they use the best Intel chipsets. So what, as far as I know, Intel still sells those chipsets to other OEMs. By the way Apple hardware usually has inferior price/GPU performance, so I am not sure where you were going with the premium part tangent.
You can't buy a Camry with a 3UZ-FE engine, or a Civic with a C30A. Apple is taking more or less off the shelf hardware and packaging it in a sleek solid feeling case. PC OEMs have seen their success and copied ideas here and there, and almost always do it for a lower price.