In the 4-6 story line, the whole scenario in ROTJ works a little better. We have to imagine what the power of the Dark Side is. We dont have the Sith "rule of two", so we don't know the Emperor plans to replace Vader until the end, and this makes Vader less of a willing participant in his own demise.
Lucas bothered to change dialog on the ESB DVD so that Vader is trying to hide Luke from the Emperor. But he did nothing to change Vader's motives in ROTJ.
The more I think about this stuff, the more I get depressed.