Not sure
I am not sure, Ben. @Noemi will know.
As for pieces of material, again you are correct. “Except where otherwise noted, content on this site is licensed under a Creative Commons Attribution 3.0 Unported License…” [source]. It also makes sense from an interoperability perspective: when the server gives you a page, it is remixing material from different repositories and in different formats, including text, images and markup. If the licenses on the different components were different, it would become a nightmare to figure out who can see what. So we just stick the same default license on everything.