You can't get to the engine without pulling it out from underneath, and yet Porsche owners and mechanics are both perfectly happy with the situation.
The majority of cars are FWD and stick the engine in the under the hood where it's easy to get at because practicality is more important.
The only argument here is for the GPU. Apple has put in a lot of work to maximize usability by targeting a specific GPU/CPU combo. RAM is a constant that doesn't really play into the design of the OS, since all RAM manufacturers make the same thing, but with different guarantees.
RAM is about the easiest thing to upgrade, second maybe to a hard-drive. This used to be trivial to upgrade, but now they're making it unnecessarily difficult to lock in customers to paying out the nose for something that should be a simple and cheap upgrade. They're operating on insane margins in the RAM arena (and CPU arena, but that's a different story).
In fact there are attempts to limit the serviceability of cars, and these attempts are harmful to independent mechanics.