See, that would make sense if it was something like 'our system must have 99.9% uptime'. But to say it cannot have any downtime, at the same time as our releases requiring us to take it down during the release, and at the same time the business contracts allowing for downtime for releases, means that the NFRs do not have any realistic requirements and are thus useless.

It's like saying mobile devices must be supported. Does that mean only top of the line recent releases? Does that mean 8 year old smartphones? Does that mean the internet browser on the Nintendo DS?