Is the Theory True?

In a recent "letter to the editor" I found this line of thinking quite reasonable (I'm not sure about his syntax) . . . .

The writer said, "While I enjoyed Leonard Pitts takiing Pat Robertson to task, I take issue with his statement, 'gravity is just a theory, but I don't hear anyone arguing with Isaac Newton'. Sir Isaac Newton's theory is, in fact, known to be wrong. For example, it does not correctly explain the orbit of Mercury. Why teach it then? Because it is useful - it does allow the prediction of motion of the planets, and NASA's spacecraft, as accurately as makes no difference. Einsteins general theory would be much harder to use and unless a spacecraft was very close to the sun, would not give better answers. Perhaps it is best not to talk about whether a a scientific theory is 'true', but instead ask if it provides a useful explanation of the observed facts."

There.