No, they make the upgrades expensive so that everyone irrespective of their income can pay the maximum amount of money they have available. The need for vastly different price points comes first and then you need to consider, how the expensive models should differ from the cheaper ones? Good speakers and metal enclosure aren't expensive. Aluminium is one of the most abundant metals in the earth’s crust. And once designed Apple literally goes to the cheapest Chinese supplier to mass-produce their speakers. Furthermore the non-pro devices like the MacBook Air do indeed have worse screen technology.
PC makers compete on the basis of spreadsheet comparisons, where the larger number on the same row is supposed to signal a better product. Quantifiable numbers are easier to compare for bean counters. Especially when there are way too many options to compare. That's how we got into the Gigahertz race and Megapixel cameras etc. The PC market trapped themselves in this cycle, where efficiency and elegance don't count. Just more of something for less money. Apple is almost trolling them with their pricing scheme.
