> What does transparent mean here?

Transparent as a system/box can be, meaning that you can't see / know about it. (Yeah, I guess you can read that not transparent as obscure in disclosure of how their system works, but it shouldn't make much sense)

> AWS is super clear what resources are zonal and provides tons of guidance around making things multi-AZ.

Yeah, they allow people cheaping out for zonal resources and then going down with their zone.