New does not exactly equate to innovation. Making a desktop computer razor thin really has not upsides, its apple's decision to opt for form over function...Limiting accessibility is basically Apple turning to planned obsolesce. They are basically limiting how much consumers can upgrade the computer at a later day and also restricting what you can actually repair. I find not positives with this move at all....
This issue is not new and was debated inside and outside Apple when the first Mac was designed in 1984. Jobs wanted simplicity and felt expansion could be handled via higher speed external interfaces. Burrell Smith who designed the original Mac logic board was always trying to sneak in ways it could be expanded and Jobs was always trying to stamp those out. Fast forward to today and that same philosophy permeates the iMac, nMP, iPhone and iPad design.
Job's zen-like focus on simplicity has certain advantages. E.g, the Apple.com site is very easy to understand and configure a machine, whereas Dell's site is a complicated, confusing mess. Apple has one version of OS X and FCP X vs other companies that have fragmented products with junior, educational, senior, pro, super-pro, etc. versions.
There is a valid argument that internal hardware expansion (whether battery, CPU, GPU, SSD, etc) entails cost, design risk and potentially degrades reliability. You have to provide access ports, slots, etc. This constrains the design and adds space and volume.
In an era of 4k video, not having an internal DVD drive in the iMac is probably the right choice. DVD is only 720x480 and produces 1/6th the resolution of 1080p and 1/24th the resolution of UHD 4k.
I also see the other side about why emphasize extreme thinness on a desktop computer if accepting a little thicker design might enable better expandability, cooling, etc. However the top-spec 2015 iMac 27 does pretty well on a broad range of tasks. It is *much* faster than my 4Ghz Windows PC which has 1TB SSD and an older i7-875K. It is vastly quieter, despite the PC having super-quiet Noctua fans.
So despite the thinness, great progress has been made and is continuing. Even though a thicker iMac might be yet again a little faster or more expandable, the current design is very impressive. Just as in 1984, today when you get an iMac you just have to accept Apple's design approach.
I think it impacts nMP users more significantly since those are so expensive and often have a longer operational deployment in professional use. Look at how many cMP users have upgraded their machines, yet that is not nearly as feasible for the nMP. It will be interesting to see the revised nMP next year and what options exist for current nMP owners.