Yes, there are plenty of solid arguments for eliminating all mechanical switches and knobs in favor of touchscreen displays. It's the fundamental reason the smartphone has been so successful. However, so long as a computing device needs to be reset/restarted from a non-functioning state, physical/mechanical switches continue to have an important function. Two switches seems to be the minimum on heavily-handled devices like smartphones and watches, to reduce the chance of accidental resets. A reset where the user's body is used to complete the circuit is at least possible, but again, preventing accidental activation is a challenge.
This is why I often laugh at those button-haters. I would love to see how those button-less devices reset itself when software is broken. I can see Apple use only digital crowns as the switch or reset button though.