Re: Not sure the purpose is lockdown
But I am. The purpose is lockdown. Jobs is gone now, but he made a point -- all the way back to the original Macs -- of keeping them locked down. People nearly got fired when he found out the PDS slot was NOT just some kind of debug slot but was for potential expansion. He chose to use unusual type screws SPECIFICALLY because he wanted people to treat machines as a sealed appliance, not an expandable computer. Note, the Mac II had loads of slots (like 8 or so Nubus and tons of RAM slots), but it was originally designed for a joint venture with Apollo Computers so they were dictating it being expandable. During the years of fairly generic beige PCI-bus systems, Jobs was not at Apple. When he came back it was all sealed up Imacs and such again as much as possible (some got used to shoving extra hard disks, memory, and expansion cards into their systems so I must admit some towers continued to be built).
Why did Jobs want non-expandability so much? I have no idea, it's just one of those things. I *DON'T* think it was something cynical like "Oh, if they can't work on their own Mac they'll buy more service from Apple and replace that Mac earlier".
Straight-up, the purpose is lockdown. Small machines can be hard to work on, but Apple at worst makes it intentionally hard to work on, and at best just doesn't make maintainability or upgradeability enter their mind when they design a system.
Will this change in the future? Hopefully. I don't know how long Apple works on chassis designs before they are released, so the current models could still be heavily Jobs-influenced.