Earlier quoted context omitted.
I'm not sure a touch sensitive button is a lower cost component than a physical button, you need an IC to drive a touch button. I can't see this being driven by cost savings. I'm not even convinced there would be a cost saving when you take into account buttons failing and needing to be replaced. Reducing the number of buttons and replacing them with on screen-only (say move to on screen-only volume) would be a clear…
Removing anything "mechanical" is a huge cost saver and a massive reliability improver. Those buttons require special drilling and machining steps on the case. Removing those speeds up the production of cases by a lot which equals cost. Mechanical switches are way more expensive than huge areas of silicon chip. It's not even close. Finally, solid-state touch sensitive stuff effectively never fails. It never gets dirt…
There would still be side operations during machining of the case to make the raised profile (I assume there still will be one you can feel). And if anything that means more waste material. That or they still have an insert.
Maybe at Apple scale they can be similar in cost, but I don't believe there is a significant cost saving at all.