Hi Brian, interesting review, and I just watched your interview with Robert Peston on quantum mechanics, which I found very illuminating (well, with a high degree of probability, anyway).
I suppose I think your review a little harsh, but this is something of the second (or third) album problem suffered by so many musicians. The first freakonomics book was informed by 15-20 years of Leavitt's earliest (and perhaps most creative)work. The second, while introducing some new material (as I recollect) expanded on that work. We might have another 20 years to go before he has anything like the same amount of fresh material. Sadly, though I find the podcasts very entertaining, I fear they will never be able to match the impact that their first book had.
As for it not being economics, have to disagree about that bit. It is firmly based on micro-economic analysis - Leavitt is quite open that macro-economics doesn't interest him very much. Economics is the study of how people behave in the face of limited resources and varying incentives. Sometimes those incentives are non-financial, or are clouded by non-financial considerations - like the sumo wrestlers (in book 1 - or was it 2), and like the footballer in Chapter 1 of this book. Statistics is an essential element of the analysis of data - not essential to theoretical economics, perhaps, but an essential part of the applied discipline. Psychology is the other element of trying to explain the pattern that the data demonstrate, I grant you. I doubt that Uni of Chicago would retain Prof Leavitt if they didn't think he was doing economics.
I'm going to see Tim Harford interview the two Steves on Tuesday evening - are you going by any chance?