Very bad example. Wall clock battery can last a decade. Any isolated power supply will waste much more energy. Also the clock will stop when the power is out.
That may be a bad example, but your analysis seems valuable. Can you think of some easy cases where batteries make sense vs. where they should be avoided?
Sorry if i do not have better examples. I do not like to replace batteries so i didn't buy many devices that would require it.
Not to mention the obvious aesthetic issue of a wire running down your wall. This is big part of wireless everything.