Trivia: In the scene where R2D2 is having his restraining bolt attached the tool that is used is a small brazing tool you can pick up at any Radio Shack.
Trivia: The wide-angle shots of the rebel base before the final battle and before the award ceremony at the end of the film show buildings rising out of a jungle. These are shots of the ancient Mayan city of Tikal, now part of the Tikal National Park located in Guatemala. (01:38:15 - 01:58:25)
Trivia: If you compare the battle between Darth Vader and Obi-Wan in this one to the battles in Episode 1, this fight seems very slow and careful. There's a couple of reasons for this - partly, while David Prowse got replaced by an expert sword fighter (Darth Vader was played by, in total, about 5 or 6 people for different things like stunts, voice, etc.), Alec Guinness had to stay himself, and he probably wasn't capable of leaping all over the place. However, more important is the fact that the lit up blades of the lightsabers in Episode 4 were made of wooden doweling (not unlike a broom handle) and if they hit them together, they snapped. These were replaced in the subsequent films with much stronger carbon fibre rods (similar to fishing rods) which explains the ferocity of the lightsaber duels in the later films. The motor within the handle spun the blade which was wrapped in reflective tape, creating the flickering effect. This only showed up when the lighting used was at the right angle. Thus during the Ben / Vader duel it explains why their lightsabers disappear at various points when they point the blade almost directly at the camera.
Trivia: Twentieth Century Fox let Lucas keep the rights to all toy merchandise as they thought the film would flop. The profits from that deal enabled him to set up Lucasfilm.
Trivia: George Lucas was so sure the film would flop, he didn't attend the premiere and instead took a vacation with Steven Spielberg, where they conceived Raiders of the Lost Ark.
Trivia: Nick Nolte was considered for the role of Han Solo.
Trivia: For a decent replica Star Wars laser sound, hold one end of a metal Slinky around your ear, and let the other end drop and hit the floor. It is neat. I would suggest you avoid letting others see you do this unless you have a chance to explain! The real sound was made by striking a metal stabilizing cable of a high tension wire electrical tower.
Trivia: When Luke is being attacked by a Tusken Raider in the Jundland Wastes, the terrified look on Mark Hamill's face is real. Stuntman Peter Diamond could not see behind the Tusken mask and therefore it was up to Hamill to avoid every blow.
Trivia: Not really a mistake, but apparently if you go up to a telegraph pole and hit one of the metal wire support cables with a piece of solid copper it will make a laser blaster sound. I take no responsibility for major internal or external injuries or loss of respect from peers. For a safer alternative, if you have a spring type garage door just tap (or even flick with your finger) the spring.
Trivia: The sound of a TIE Fighter engine is a combination of an elephant bellow and a car driving on a wet pavement.
Trivia: Lightsabers are made out of a selection of camera parts - you can get the schematics for them on the internet, and make your own. However, the right camera parts are very hard to get hold of, because firstly they were around in the 70's/80's, and also because Star Wars fans keep buying them.
Trivia: Alec Guinness was the first actor to be paid a percentage of the films takings and toy merchandise as he thought the film would flop. The other actors were paid a wage until the second film, then they opted for the same as Guinness.
Trivia: Although they play the body and voice of Darth Vader, and have spoken on the phone, David Prowse and James Earl Jones never met until about 2012.
Trivia: The huge alien skeleton that C-3PO passes in Tatooine was left in the desert by the crew. When they returned to the area in the year 2000 to make "Star Wars: Episode II - Attack of the Clones", the skeleton was still there 23 years later.
Trivia: The film was almost cancelled on the first day when Tunisia experienced its worst desert storm in half a century, destroying most of the set.
Answer: It is heavily implied that one who becomes a Force-Ghost achieves an untold level of power upon entering the state. Given that they have become a pure entity of the Force, it seems to back up the statement. Obi-Wan also becomes free to assist Luke in any case.
Darius Angel
In addition to this answer, I think Obi-wan also became powerful because he "let go." He did not feel a need to defeat Vader on this occasion - he was willing to surrender the fight and "move on" to a new state. Something that Vader might not currently understand.