Beyond the technical differences already mentioned, there's also the difference in consent. The 8-16GB of dormant AI data is either on your $2K 128GB device, or it's not.
In this regard, Apple did not learn from the free U2 album they automatically added to everyone's iTunes account at no charge.
There was enough outrage at the lack of consent in that decision, Apple had to create a special support path for removing it from accounts.
Given the divisive opinions about AI, it's odd Apple didn't include a "delete" button to completely remove it from your device if you wish.
https://web.archive.org/web/20141116221641/https%3A//support...