The US entry for pets in cabin has a note about pets in the hold and conflicting information on the pets in the hold section.
Here's is US's policy, as confusing as it may seem: Pets in cargo compartment
For the safety of your pet, US Airways does not accept any animals in its cargo compartments.
Exception cities
US Airways accepts dogs, domestic cats and birds as checked baggage on nonstop US Airways Shuttle flights in the BOS/DCA/LGA markets only. Connections are not permitted. The customer must travel on the same flight. Customers should advise US Airways when they wish to transport a pet as checked baggage on a US Airways Shuttle flight.