Well clearly that crowd sees some advantage in a "chessboard" sort of way. By weaking the leverage of the (largely) center/center-right "Larry Sommers-like" World Bank they strengthen the relative hand of the more reliably monetorist IMF. Moving the WB towards grants also removes the rationale for a UN role (look for a 'why should there be a UNDP' campaign?)
((Of course they also have designs for the IMF, but that is another story.))
Actually it is probably closer to something like: by giving the more wimpish BWI wing a good kick it reminds them that Sommers (never mind Stiglitz) should be left far behind. We should also remember that Wolfonson is a Clinton appointee so its fair game; once they get their own person in there (and this might speed that up) then it is much harder to pull some of the rug out.
Plus, of course it throws a bone to the more isolationist right and reminds Europe and Japan that they shouldn't demand too much from U.S. multilateral participation.
Their calculation should not be ours, but I would imagine it runs along these lines.
Paul