Tirade - Cheap Fares

What the heck is with these airlines?  The other day I arrived early at an airport and went up to the ticket clerk who was amusing herself watching people struggle with the "do-it-yourself" computer in front of her desk - they don't check you in any more, just watch you struggle.  I showed her my printed out boarding card, done at home, of course, and asked if I could get on an earlier flight.  She directed her attention to her own screen and punched some buttons.  "There's one in half an hour."  "That would be great," I replied.  But wait.  "Oh, your ticket is a reduced fare one."  This said as if I had a particularly virulent and visible form of venereal disease.  "There's an additional charge for that, I'm afraid."  "Oh really," I said, "what might that be?"  "$125!"  Good grief!
Now what's the idea behind the penalty. Are we supposed to buy more expensive tickets than the ones they advertise so that we can chop and change around?  It seems a little draconian to me.  Come on People!