of future clockmaking

In the spirit of our current book of the month, I thought I'd throw out a link to The Long Now Foundation. For a literary introduction, here's what Michael Chabon has to say about it.

I actually saw some of these prototype clocks at the Fort Mason Center museum in San Francisco, a year or so ago.

Here's a question: is the idea to use mechanical guts for this clock of ten thousand years based mainly on nostalgia for the past? Are there technical reasons why a more "solid state" solution wouldn't work? Ok, we've been using atomic clocks as a time standard since 1967, but could one of them last for ten thousand years on its own, in a cave in Nevada? Beyond the question of technical feasibility, is there something more human, more understandable, to using mechanical gears, rather than the frequency of cesium electronic transition radiation for the basis of time keeping?