No, they just let it ride and hope nothing breaks.

I know you're being sarcastic but you're probably more right than you realize. Many many "redundant" systems turn out to not be so redundant when it counts.

talk to some datacenter admins and you'll learn there's a lot more bailing wire and hope-for-the-best out there than you would think.

Wonder no more, the answer is: yes, obviously

Someone is always signing off on routine tests.

Same deal as those 50 point inspections your mechanic does: some things are easier to inspect than others, some people do a more thorough job than others, etc.

Yes and frequently.