It's how everyone remembers it in their mind until they re-watch the film. I just realised though, why does Obi Wan disappear? Lucas done a massive shit on people in that scene or what? Attempting to leave it open for Obi Wan to come back with the universe rules not set yet but went with the smiling Ben martyring himself, knowing Luke is the true heir of the prophecy or did he just later decide a Jedi's death wasn't to be a vanishing or was Obi Wan even the first to die from light saber who wasn't in a white plastic shell... I'm really kind bummed out now but alas, all things are flawed.