Rhikter said:
I think it's perfectly reasonable to suspect that 3PO had some hardware upgrades in between the films. Take into account how old he really is and how many times the poor fellow has been blown to pieces.

I never had a problem with 3P0's mid section being straight rods and wires in ROTJ either. If anything, it makes perfect sense. That was one of the main points he was severed at when he got blasted back on Cloud City, so it makes sense that it in putting him back together, it was easier to just rip out all the straggly wires and start fresh. Yeah, R2 patched him back together in the Falcon during the escape, but that was just that - a patch job. Luke would probably have gone back later to do some more work on him.