Can't say I blame GL for not being happy with the draft. It's terrible; at least the depiction of Han is, rather. All of his lines come across as "Gosh golly gee wiz, we sure don't know what we're doing here, see" (in 40's gangster accent).
I always noted how similar Luke's green ROJ saber is to Kenobi's ANH saber. This stands to reason, as it was made with parts recovered from Kenobi's hut. But I also took it to mean that Luke was 'emulating Ben' a little more in his use of the Force, and this manifestation of it.
Old eu now legends stuff has that Luke found an old leather bond book in kenobis home when preparing the han rescue and built it off those plans.
The production answer is probably that there was a tighter budget and lightsabers, being a new concept themselves, didn't really have much innovation in this first form of their existence. For Luke's and Vader's, they both used the camera parts, but used different cameras, to make them "different" (now we've seen a wider assortment of hilts, but they were still different enough for this first movie). Since Kenobi was the master of Vader, and trainer of Luke, he got the "cooler" lightsaber.
There are some differences though Above is lukes rotj saber Obi wans saber from rots, Luke's has the d ring attachment, which obiwans will have in a new hope. obi-wans has a bit more black then lukes which has silver highlights on the hand grip. Lukes saber has a slightly different emitter as well. Both Of the above also seem like a simplified wartime evolution of Kenobi's saber from tpm and aotc All have an actual pommel and the the round hand guard things, as does qui gons hilt. Surprisngly the jedi with the most similar design to anakins hilt is yoda
The story I heard was that Luke's saber prop was taken from Obi-wan's, but aside from those minor changes, the major difference was that the rod used for the blade was left inside the hand grip, after being sawed off. Hence the bit that sticks out.
Cool makes sense with what we know about how lightsaber effect was created in each film, from spinning rods with film screen material in a new hope, the improving carbon fiber ones they used in the other films. They got to episode three and rather than being worried about the rods breaking or bending as in the other 5 films they had to worry about the actors getti hurt as the material had gotten strong enough to withstand the abuse but left Ewan, Hayden, SLJ, and the stunt guys covered in bruises during preproduction per making of rots. Watch ewan mcgregor and ray park train below with aluminum rods in the below footage from the begining documentary Now watch Ewan Mcgregor and Hayden Christiansen training for episode 3 Bit of a difference but not much. Ewan was always that fast and Hayden caught up to Ewans speed with the fighting in rots
One thing I like is that the old eu had an explaination for the styles of hilts. The Anakin type of hilt is for some one that uses form V Djem So or its Shein variant. this is why Ashoka has a saber that is very similar to anakins even before she meets him because she also uses Form V but the Shien variant with a reverse grip. Starkiller also uses a very similar style of hilt in his video games. with that little stop pice at the end to prevent the hand sliding down. Anakin Vader Ahsoka which is a cool combo of element of Anakins saber and Obi-wans 1st lightsaber with the pommel JK sabers version of Starkillers saber based of of images from the game.
Another question I have about similarity in lightsabers is the Emperor's comment in RotJ (after Vader hands him Luke's lightsaber): "Ah, yes, a Jedi's weapon. Much like your father's. By now you must know your father can never be turned from the dark side. So will it be with you." How, really, is Luke's RotJ lightsaber like Vaders? Could the Emperor be referring to Anakin's, that Luke uses through ESB? Doesn't seem likely, and those don't appear similar either. Perhaps a few things are going on here. The rest of the Emperor's little speech goes on to compare Luke and Vader, saying how similar they are and how Luke will follow in his father's footsteps. He also uses his lightsaber talk to highlight for Luke (and perhaps indirectly to Vader himself?) that there is NO WAY that Vader can be redeemed.
What about Starkillers TFU II sabers? Did they look similar? Also I know that his Sith Master version has 3 prongs and a striped black area at the base, similar to Anakin's. I know because it's my favourite saber design.