As far as I can tell, the preferred PURL domain setting (and also the preferred pastebin domain) are not exposed in the API. This means that a client cannot properly generate links to view or copy to access these resources. (They can make generic links for url.lol and paste.lol since they know the address, but that may not match the user’s preference). Exposing these settings in the API would allow users to experience the same behavior in a client as they can on the web.
Great catch — gotta have this. Will get it going ASAP.