Very interesting site, Chris - it will also be interesting to see how the rankings change as other things come on line.
Your point about the lack of communication among the various areas of the 'information field' is also spot on - this is one of the things that IR is trying to change, by publishing information systems papers, as well as information management papers. David Ellis, David Allen and I wrote a paper a couple of years or so ago which looked at the lack of cross citation between information science and information systems in two areas where one might expect common interests - information retrieval and information seeking behaviour (user requirements in info. systems parlance). We found very few people who were cited in both fields.
Ellis, D., Allen, D.K. & Wilson, T.D. (1999)
Information science and information systems: conjunct subjects disjunct disciplines. Journal of the American Society for Information Science, 50, 1095-1107