I don't know if this was a bit of convenience to avoid a plot discontinuity, but if so, it works. The Jedi were blind to their own weaknesses, and this was one of them.
Obi-Wan told Luke that Vader killed his father in order to keep Luke from running off to confront Vader, knowing that confrontation would provide an opening to allow Vader to turn Luke. That is completely rational -- if you don't understand the power of emotion.
However, once you take emotion into play, this actually gave Vader and the Emporer a powerful card. Unfortunately for them, and despite the Jedi's attempt to keep the truth from Luke, the truth of Anikin's actual fall was what saved Luke in the end.
Huh? There's nothing in any of the movies that suggests this. Obi Wan has concealed his identity for years, straight up lies to and mind controls a couple of Stormtroopers, and is more than sightly shady in his dealings with Han. Heck, it's pretty clear that he had figured out what happened to the Jawas long before Luke did and intentionally withheld the information because he thought Luke would would do something rash - exactly the same thing he did regarding Vader's identity. And that's just in the original movie. In Empire, Yoda quite deliberately gives Luke a false impression of who and what he is ("Take you to him I will", "Yoda not far", "Soon you will be with him") and tells Luke that the lessons are finished for the day immediately before sending him into the cave to confront the Luke/Vader vision.
Jedi have always been more than willing to bend or ignore the truth.
I liked the movie more than most, but one of the things I was always disappointed in regarding Episode III was that there wasn't a scene, that was in the novelization, where Yoda realizes how much of a mistake he made in having rigid rules for the Jedi regarding marriage and families (btw, the novelization is awesome). I mean, how many of us were rolling our eyes when Yoda's solution for Anakin is to "rejoice" when people die?
There are a number of websites that have copies of the revised fourth draft of the Star Wars script that include the subtitle "Episode IV: A New Hope." This website even appears to have a (low quality) photograph of a copy of that script autographed by the cast.
http://mysterymanonfilm.blogspot.com...-time-ago.html
A lot of other sites have the script in text format (for example here http://www.blueharvest.net/scoops/anh-script.shtml) but of course it would be difficult to prove that the presence of the subtitle was there originally.
Unfortunately that photograph is the only one I can find.
This site here (http://starwarz.com/starkiller/) has many of the early scripts (I can only assume what is there is accurate). You can even see that in 1975 George Lucas had the idea of an episode number in mind:
The Adventures of the Starkiller
Episode One: The Star Wars
Be that as it may, it will always be "Star Wars" to me.