SteveFehr quote:
Nope, no walls or separation like that in the US, it's all just jammed in there pretty much however the installer feels like. In fact, this is the first time I've ever heard of that! How does that work, doesn't that really put a crimper on how you can route cables into the panel?

Big time! You can only terminate a cable through the knockouts below the main breaker. Cannot come through the top. Only the mains and the main ground can be in there. In the installation you show, we would have to bring all those NM's around and through ko's on the side or bottom of the panel. Mabey even install the panel upside down?