Today's Wall Street Journal has an interview with Burger Kind CEO John Chidsey. I found this passage, where he explains why fast food companies are thriving, pretty telling:

If you look in the fast-food hamburger space, it is unfortunate for the greater economy as a whole, but we benefit from the pressure people feel from a disposable-income standpoint. People who cannot afford to go to Applebee's, cannot afford to go to Chili's, we are the beneficiaries of that squeeze.

--Jonathan Chait