I agree. And that's exactly one of the big changes that are happening. Prices for hardware components and manufacturing are dropping and we now have the ability to think about more suitable interfaces. I stopped using my lifx after a week because I did not have a fast and simple interface to control them.
Clearly the reason many connected devices expect you to bring your own screen is cost - Nest notwithstanding, adding touchscreens to everything when you've already got one in your pocket seems unnecessary, and would clearly add to price of these products.