As asey correctly points out, the link I posted talks about the Cloud SQL maintenance window, not about Compute Engine. That there is unavoidable downtime even with HA has been a problem known for seven months at this point. A Cloud SQL TL even sought feedback here with people telling that person this is a "dealbreaker" and another saying it doesn't even make sense to have built HA for a low probability event (zone outage) before dealing with this much higher probability event:

https://news.ycombinator.com/threads?id=flamingcow

This is pretty strong customer feedback. What happened with this feedback, anything? The bigger picture here about GCP, preceded by Google's long reputation, is that customer feedback means nothing. Googlers are probably still building what they feel like building, and that is why AWS continues to trot ahead despite being less polished. They ship things that work and they know what their customers want.

One example fitting GP description would be Cloud SQL maintenance windows. Unavoidable downtime as far as I know (even with HA)