I can't imagine it works any differently for any other high-volume manufacturer. Most packages are designed to include the most popularly-chosen options in order to simplify the production/ordering process. Having someone order the heated seats but not the heated mirrors means you're likely having to keep a custom trim or control-unit that omits those options, which is increased inventory for a rarely-optioned vehicle. Inventory costs are a killer for manufacturing, so lumping options into packages helps keep lesser-chosen options from having the inventory associated with it pile up unused.
Also, the thing that is increasingly difficult to do from an aftermarket perspective, is the integration. Prior to this decade, many of the electronic options were separate modules that could be added on fairly easily. Now, most vehicles use a central nav screen to control HVAC/heated/cooled seats, and a slew of other options. This means simply buying a base model vehicle and adding a lot of aftermarket goodies is much more difficult because it has to inter-phase with a dozen different systems, which is almost impossible for aftermarket manufacturers to adapt to. Even adding a subwoofer can be a royal PITA if the head unit from the factory isn't equipped for it.
If this is a Ferrari, there's likely a lot more flexibility with low-volume vehicles as well as a shorter list of options. You pay dearly for that!
