I like how John Siracusa explains the concept of "naked robotic core"
To paraphrase, the phone is the computing unit, and the user customizes it to fit it's usage.
People that never dropped a phone in their life can use it as is. People who work in construction can put hardcore shells that survive multiple floor drops. Those who like furry cases can go wild and those who want to build accessories around the phone have a smaller target to do so.
Seeing it this way, having the phone thin enough than you can put the case you want without the whole package being bulky is a feature.
To touch on the laptops, a few grams shoved off won't matter and don't justify a huge sacrifice. But the size and weight drop we had from the 15" Lombard laptops to today's 15" don't all happen in dramatically, and keeping a goal of having the next machine thinner than the previous one can help achieve huge progress in the long term.
I am not a fan of the current keyboards, but I can't throw them the stone for trying to make things thinner and lighter. I was super happy to see the lighter 2013~2015 models, and I don't want them to just settle and say "we're good enough for the next 20 years, we don't care anymore".