The prologue in the book version of A New Hope is supposed to be a piece of history text called "Journal of the Whills", which were supposed to be some kind of tranccendental species of beings (kinda like hyperintelligent shade of blue) that were supposedly closely related to the Force and lived kinda on another plane of existence just connected to the galaxy far far away universe via the Force.
A lot of things changed from the earliest ideas to the abhorrent display of greed and indifference that was the prequel trilogy. The Whills were dropped out pretty much completely (aside from a comment from Qui-Gon's spirit to Yoda - apparently the Whills were the ones who discovered how to join the Force without losing one's individuality), and Force was de-mystified via midi-chlorians at some stage of plot developement - it was originally supposed to be a lot more spiritual than what it ended up as... Lightsabers were supposed to be really heavy, Skywalker was supposed to be Starkiller, and Han was supposed to shoot first. Palpatine, I guess, changed just as well, from a puppet ruler into a manipulating tyrant.
Ironically, I think the story behind Palpatine became better for the changes they made in that regard. It's definitely a plot change too - if it were an ordinary history text in the prologue, I'd chalk it into a misconception of history but due to being a quote from this "Journal of the Whills" it's supposed to be accurate... therefore it's just one more thing that was changed.