1) Comfort. Like Obama, Geithner is 47 (Obama is 14 days older), a fast riser and a technocrat.
2) Multipolar. If Larry Summers takes a White House post, you will have two bright academics (Summers, Bernanke) along with a bureaucrat running U.S. economic policy. It would be nice to have someone with business experience in the mix, yes?
3) Condi II. I wonder if Geithner will end up a mediator of sorts between competing economic centers of power such as Summers and Bernanke. Geithner strikes me as an executor of policy not a creator. And fiscal policy would seem to reside in the White House.