> The key seems to be truly independent failure domains - something NORAD achieved through physical separation that's harder to replicate in cloud environments.

It's not hard to achieve separation in cloud environments. It's just expensive, and for most, the need doesn't justify the expense. Every once in a while you do run into things like actually all the clouds in (location) are located in the same building; or you paid for two separate strands, but a backhoe has determined that both strands are in the same bundle. Or your two redundant providers of whatever use each other to provide service.