I find it extremely interesting that they'll be using natural gas as their primary energy source for the campus and using the electrical grid as their backup. Is this really cost effective? Are many businesses doing this?
Beyond that, the cost comes down to availability. There are parts of the world where every single house has a natural gas line for heating (water and air). I've heard that in Japan, small/clean/quiet (relatively) generators are installed in some apartments and provide electricity.
This article has some information on natural gas usage in California. It seems like most of it come from out of state (or country): http://www.cpuc.ca.gov/puc/energy/gas/natgasandca.htm