CVG is similar, with half of the terminal/concourse buildings currently closed. However, in both cases the airports have been de-hubbed. The capacity that is now surplus was there to serve connecting passengers and flights that now flow through other hubs. If the facilities had been sized to serve only the local population, they would never have been built out to their present size. The underutilization that afigg predicted doesn't really apply here because the capacity was never intended just to serve passengers to/from PIT, but passengers connecting through the airline's overall network.Pittsburgh International (only such because you can get one of two direct flights to Toronto and seasonal service to Paris) has already closed the entire E-Terminal. 50% of B-terminal is closed and over 50% of A-terminal is closed. We're not some rural airport, we have 2.5 million people in the area, plus we get travelers from Northern West Virginia and South Eastern Ohio.
I think afigg's point was directed more at smaller airports such as CAK, which could suffer if (for example) Southwest pulls the AirTran flights and serves the area only from CLE. If that happens we could see other airlines raise prices and reduce capacity and destinations, forcing more traffic away from CAK and toward CLE/CMH/PIT and eventually creating a situation where CAK is seriously underutilized.