Since the landing page required everyone interested to enter a keyword to search, the back-end server can record all query and ip-addrs.

I doubt if WikiLeaks.org use this exact same method to study what document attract traffic|attention. WikiLeaks' new releases are not signed by PGP anymore, I take that as either a Warrant Canary or some kinds of warning.

Of course, if everything packed in a torrent, then there's no way to conduct such a study.