Imagine this scenario. Peak traffic time in the day and site goes down because of a deployment, an investor sees it and threatens to pull money out. Ad networks that you work with actually see a report where during peak hours their advertisements weren't served, causes of major trouble. I work for one of the biggest sites in my region and take my word for it, uptime is essential and not something left to chance or gods.

Continuous deployments ensure delivery of features and turn around time fast enough for a changing business model of startup and can't be stopped either.

So uptime and continuous deployment model has to happen at the same time.

Deployments should always be automated and revertable. If you think you can run a healthy startup with just about adequate mistakes perhaps you got an easier place to work at :)