If you're building services that still require "regular maintenance windows" in 2014, you're doing it wrong.
This is a really nice sentiment but is in fact somewhat disconnected from reality.
In the web world, building zero downtime services that don't require maintenance is doable. In many enterprise IT environments with legacy or bloated software (hospitals, education, government) it's a non-starter. The staff do not have the skill, the applications don't have the support, and the political will within the organization is not there. Database migrations alone can be a major source of downtime, and that's largely true even for web services.