I still don't see the point in the stupid new iMac. Big deal, it's thinner....because everyone NEEDED a thinner DESKTOP machine?!
I addressed this a few pages back. You're thinking about this backwards.
It's not that

made it thinner. It's that

made what the technology warrants, and did it well.
Laminate the screen to reduce reflections, get a good 21" HDTV-resolution display ... hey, it's really thin.
Select CPU, RAM, GPU, & storage more than adequate for most users, with a few variations on each, all fits in about the space of two stacked card decks ... hey, the guts are really small.
Look at how you can put the two together, take into account efficiency, manufacturing, and aesthetics ... hey, it's an AIO with crazy-thin edges and a modest bump in the center back.
Revisit the old axioms and re-evaluate them.
Most users never upgrade anything in the machine. If they do, it's internal RAM mostly on larger units. With superfast Thunderbolt and USB3, way easier to just plug in an external drive for more storage. If a little slower than screaming fast is acceptable, zero-installation wireless network drives are even easier. All internal hardware is optimized for the processor, so there's not much value in enabling a user to install a future CPU of questionable compatibility.
All that vs. the benefit most customers get from a machine built efficiently to specifications, and no space/cost wasted on rarely-used error-prone upgrade modularity.
So...decide what the unit's specs will be, and build exactly to that for optimum manufacturing cost, maximize what most users want and minimize unwanted/unneeded overhead. Result: compact & thin.
"But repairs!"
Most users don't repair their computer. Most repair centers won't have the optimized components (just like most auto repair shops don't stock BMW parts). Supply chain for repairs is costly & complex, keeping numerous parts on hand for speculative need, and requiring training of thousands with minimal oversight & talent.
So eliminate the repair supply chain. Repair? Replace. Easy enough to get an identical (or even superior!) unit. Other than stored data (which can be copied if it can be copied, and is gone anyway if it can't - "got backups?"), there's no pressing need to repair that unit on the spot. Give the user a replacement from a few in-stock (or overnighted) models, copy data if possible, send broken unit to a central repair service which has all the equipment, parts, and talent needed for optimal repair & refurbishing.
Why repair? when the customer can get a certified factory-quality refurb faster than finding & fixing, with iffy results, the offending part?
It's not that

is so much obsessed with thin, it's that the technology - pushed a bit to delight most users and antagonize most competitors - leads to thin design. Everything points in that direction, so push it the rest of the way and reap the benefits.