Treasury secretaries and university presidents have quite different jobs. Treasury secretaries have (or should have) real power. For example, they can fire people who work up to several levels under them. People willingly overlook a cabinet secretary's social inadequacies because they need something from him. University presidents, on the other hand, famously have relatively little power. A university president's biggest responsibility is to coax money out of donors; to do that, s/he must have social graces. He must also win over faculty lest they make him/her look like he can't keep order in his own house and thereby harm his fund-raising ability. Faculty, many of whom (at a place like Harvard) have long-cherished outsized images of their own prowess and importance, sense that dependence and are not shy about asserting their prerogatives. And they can't be fired.
Thus, it's quite possible that Summers' social ineptitude could be a serious liability as president of Harvard and not so much as secretary of the treasury.