The story I've long heard about why Southwest doesn't charge for checked bags is that their computer system isn't equipped to handle such transactions (Their CRS is called SAAS and is based on the Braniff COWBOY CRS developed back in the 1970s.). The airline is in the process of switching to a more up to date CRS and those systems do have the ability to charge bag fees, change fees, etc. Now whether or not Southwest will actually jump on the bag fee bandwagon officially remains to be seen. Companies generally don't do things because some Wall Street types says they need to do it.
