Why do people insist that Amy didn't tell David about the rape?
Just because it's not shown onscreen doesn't mean that she doesn't tell him off screen. He comes home to find her in bed sobbing and saying that if he had been there, this would never have happened. Peckinpah didn't need to show the actual conversation between Amy and David, because it is implied. The next day David appears before the men extremely angry and tells them to get the hell off his property. This is not the small anger of a guy who just had a little prank pulled on him, this is the rage of a man whose wife has just been violated. Then, when they are at church, both David and Amy are visibly uncomfortable around the men, and when she starts crying, David seems to know exactly why she's upset and quietly leads her away. Also, during the attack on the house, when Scutt informs David that Charlie had sex with his wife, David does not act in the least bit surprised.
He knows. She told him. For whatever reason, Peckinpah chose not to show that conversation between them. Directors don't have to show everything the characters say and do, sometimes scenes are implied, like when someone is about to be killed but they don't actually show the murder.