University presidents' salaries on the upswing

Income inequality has been increasing in the US since the 1970s.  Today's NYT has a blog post by Steven Rattner looking at the pay gap between university presidents and faculty over the last decade.  Data compiled by the Chronicle of Higher Education show that at the 50 wealthiest universities faculty salaries increased by 14 percent between 2000 and 2010 while salaries of presidents increased by 75 percent. 

What have the presidents done to receive such large pay increases? Most universities still hire their presidents from a pool of academics, a pool that is the same size today as it was in 2000.  Rattner notes the possibility that the jobs of university presidents have become more demanding (which is just what CEOs of private corporations say) but (a) this is an argument that cannot be tested against data and (b) it is obviously a self-serving argument.  University presidents in the 1960s and 1970s had to deal with demonstrations and riots on campus; seems to me their jobs were much more stressful than those of their current counterparts.