Maybe Luke was too much of a wuss to respond with anger there: "My saber is nothing like his!!!"
your probably right, but you gotta remember that in the OT there were no sith. GL didn't come up with the idea of the sith until near ep1. in the OT vader was a dark jedi and lightsabers were just "a jedi's weapon" hence why palpatine made that comment to luke.
anyways back on topic. obi-wan's saber for ROTS is a slightly different design from the one in ANH. anyone who is a replica freak will be able to notice the differences besides the whole D ring thing. if anyone wants to see what i'm talking about surf the web for some replica pics of ob-wans saber before the ROTS pics came out and you'll see what i mean.
Here's Obi-Wan's ANH saber:
http://www.rebelscum.com/photo.asp?image=mr/mr-obiwanweathered4.jpg
If you compare it with the image that was posted at the top of this page, you'll see that they're different.
This is Master Replicas' version of Obi-Wan's ANH saber as it would look when he first built it:
http://www.rebelscum.com/mrobiwananhsaberasbuilt.asp
So his RotS saber isn't the final one. He has to build a new one, which we see in ANH.