We are going to take a look at the Duel on Death Star II, the duel that redeemed Anakin Skywalker, earned Luke Skywalker the title of the true Jedi Knight, destroyed Palpatine and brought balance to the Force.
We are going to see how that duel is not "short" like some people say.

Luke makes the first move by pulling his saber and hitting Vader's. After that scene, there is a scene about the Rebels and Ewoks battling Stormtroopers.
But after Han says:"I've got an idea" we suddenly see the duel continuing.
This duel is often considered "short" by Star Wars illiterates. You do not have to look closely to see that, after the scene with the Battle on Endor, we see Luke and Vader dueling 12 feet away from Palpatine, while they where right next to his face in the previous scene. This can only mean that they where dueling in the 3 minute-long interim between the two scenes. So if you have an advanced understanding of the Star Wars Galaxy, it is easy to understand and think so.
Besides, Lucas said that he cut most of the battle and he preferred to show the battle on Endor because "it was just two guys hitting each other with glowing sticks".

The ROTJ novel says that Luke and Vader are battling in front of the Emperor (before Vader's kicked off the stairs) equally matched, which means that they where dueling for 3 minutes or something.

At the start of chapter "Father vs Son", Luke and Vader look so into the duel, which means that they were battling. Plus, there is pictures on the web that show Luke battling Vader 8-9-10 feet away from the Emperor that are not included in the movie but are considered canonical.

Here are some of these pictures:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&Item=330249054278&Category=1357&_trksid=p3907.m29#ebayphotohosting
http://www.geocities.com/rushyoda/Darth_Vader___Luke_Skywalker.jpg
http://i172.photobucket.com/albums/w7/leia0organa/4.jpg
http://www.cinemasterpieces.com/revengejedi011705.jpg
http://www.starwars.com/hyperspace/member/photoreceptor/2005/02/photoreceptor20050218.html
http://www.starwarz.com/tbone/index.php?categoryid=18&p17_sectionid=103&p17_start=100
the last one is not a pic, but a gallery link, find it.
There is a pic in the following article, in the bottom:
http://www.starwarz.com/tbone/index.php?categoryid=11&p2_articleid=420
It's Luke fliping back to avoid one of Vader's blows. And it is not the flip included in the film.
there is an edited version of the photoreceptor pic which I have in my PC.
If you want it, email me: ginzitsu@gmail.com

Lucas also said:"It is bigger because of what is going on in their heads. That is what makes it bigger.'"about this duel being bigger than the duel on Bespin. With a perfect balance of skill, compassion, fury, hate and redemption, this scene set the standard for every fight that ever followed.

These are the facts that make the theory totally make sense. This theory is something simple I think, something implied with clues that almost everybody noticed before.

The duel does not look short any way, not if do not watch it a zillion times.
But now that the "interim" theory totally makes sense, it is a superlong
battle between Father and Son (like, 6 minutes).
And the cherry on top: the RotJ novel totally agrees with my sayings! It describes a very equal physical fight before Vader's knocked down the stairs... And going against the novel is going against Lucas! (I read that on Wookieepedia).

Some great articles:
http://starwars.wikia.com/wiki/Duel_on_Death_Star_II
http://www.starwarz.com/tbone/index.php?categoryid=11&p2_articleid=420

Other entries about this battle:
http://blogs.starwars.com/saberb/1
http://blogs.starwars.com/saberb/4
http://blogs.starwars.com/saberb/6
http://blogs.starwars.com/saberb/8
http://blogs.starwars.com/saberb/9
http://blogs.starwars.com/saberb/10