Good point, updated my reply. While Google don't explicitly say that they want to support run-time updates of the kernel and OS; it's implied in their system architecture that such is the case.

Very difficult to do that though without enormous effort in transparent state persistence across restarts. Restarting even something with a very simple non-transactional API and state base like a filing system requires persisting all the file handle state, and that's the best case. Restarting a UI subsystem is much harder still because the apps may have a lot of uploaded state, things may need to be changed transactionally, etc.