In Panels, how are the 2 given arguments in System's node_view created?
Panels has by default some operations on url arguments which can create variables used in Panels. The short explanation is that Panels for nodes does a node_load on the node id which is part of the url: node/[nid]. It does something similar for taxonomy terms, only depth isn't the term itself, but rather information about it.

You can do this yourself if you create a custom url with placeholders, like my-panels-url/%node and assign the variable to be a node or taxonomy term.