This is exactly the calculation apple has done; they now deem RAM to be reliable enough to not have a significant impact on warranty claim expenses. This is why they did not solder the (much less mature tech) SSD.
>I think it's more so a side-effect of the relentless push for smaller, thinner devices.
I think this is naive, personally. The extra 3d space of a RAM module on a laptop is minute. The size is a nice bonus. Also i'd bet a very significant chunk of macbook Pro owners upgraded their RAM.