It seems that Harvard's top economists are looking more to electronic dissemination of their work than they are to publication in the top journals. The explanation from Dani Rodrik's Weblog:
Several pieces of evidence bolster the view that one factor contributing to these trends is that the role of journals in disseminating research has been reduced. One is that the citation benefit to publishing in a top general-interest journal now appears to be fairly small for top-department authors. Another is that Harvard authors appear to be quite successful in garnering citations to papers that are not published in top journals. The fact that the publication declines appear to be a top-department phenomenon (as opposed to a prolific-author phenomenon) suggests that a top-department affiliation may be an important determinant of an author’s ability to sidestep the traditional journal system.
Rodrik is Editor of The Review of Economics and Statistics and he notes that his own experience as an editor of a prestigious journal supports this conclusion.