I agree with the chicken and egg analogy. I just wonder how much Lucas used the OT to setup things for the prequels. For example, did he watch individual scenes and ask, "Why/how did that happen?" In this case, did he (or other writers) ask the questioms, "Why would those creatures react at the sight of the jedi?" If he was looking to fill the gap and answer those questions, then I think the massacre scene makes sense both in Anakin's turn to the dark side and connecting it to those scenes in ANH. Again, we only see them reaction when Luke appears. I once heard an author say that when describing a scene, you don't mention the shotgun over the mantle unless someone takes it and blows someone else away with it. That particular scene just seems too intentional of a cut, to me.
And that's the beautiful thing about the Prequels! It answers so many questions that arise when you watch the OT.