Why does tennis still have line judges?

The last time I played competitive tennis my racket of choice was an old Jack Kramer (wood not metal, thank you very much); Pancho Gonzales was still alive and a hero to youngsters such as myself and the in-your-face Jimmy Connors was just arriving the scene.

In other words, a long time ago. And I'm willing to admit that my comment here is one straight from the peanut gallery. But after Serena Williams (whom I happen to think is very good for the game of tennis) lost her match in the U.S. Open over some verbal abuse with a line judge who had called Williams for a foot fault, I have to wonder: with technology what it is, why does tennis have line judges anymore? You can, without doubt, know whether a player foot faults, or whether a ball is in or out with the use of technology. In the U.S. Open, for goodness sake, why do we rely on human judgment?

Just asking.

And by the way, Jack Kramer died Saturday. You can read his obit here.

Pancho Gonzales died destitute in Las Vegas in 1995. Andre Agassi paid for his funeral.