Niraj Chokski points to historical trends in the cost of eduction:

For 27 of the past 30 years, the price of education has grown at a faster rate than that of medical care. Education also grew faster than inflation for 29 of the past 30 years, while medical care beat inflation 27 of those years.

It is easy to imagine that increase in demand is the primary driver of this trend.  It will be interesting to see how this plays out for individual schools. How will the expenditures they incurred based on the need to compete in a crowded education market (new dorms, trendy dining facilities, improved athletic facilities etc.) effect their ability to compete in a changing market.