The Cathode Corner site has a nice writeup of the design considerations for the Nixie Watch

As I pondered the perplexing problem of what to do with the back of the watch, I decided to study the mechanical watches I had lying around. They all seemed to have the same general design – a big turning with the strap lugs formed by punching out the material between them and from the sides of the watch. I had to approach it a bit differently, since I had an o-ring seal to get in the way of milling away material from the front. So I had the material milled from the rear. But I used the idea of turning the strap lugs, which is what gives it that watch-like look.

Although they figured out how to seal the case and make it attractive, battery life is still far below the paltry one-year that was planned. Hello, solar? What is that other wrist for anyway? Ironically it has a sensor built-in to save battery life by only displaying the time when viewed from a certain angle. Why not also generate energy from movement? This becomes a great example of how dependent a system is on energy, yet how little engineering is spent on solving the problem of input versus aesthetics.