I don't really buy into the whole "deleting crew/actors from the films is disrespectful" argument. Cast and Crew are fleeting in screen credit--how many crew members that worked on the films that didn't recieve credit? Daily camera assistants and camera operators, electrics and grips and art P.A.'s--hundreds of people dont have screen credit because screen credit is not given to everyone. Similarly, your work is subject to end up on the cutting room floor at a moments notice--i've shot dozens of scenes where all my hard work and the countless manhours of dozens of people has been rendered nill by its deletion from the show. Its not disrespectful, its just the way movies are made. In this case, with the edit of the film still evolving 20 years later, a few more people got cut out of the film (while adding a slew of more technitions and thespians). Its just the nature of the business.

As for Marquand, his being british had nothing to do with guild trouble--theres plenty of american directors who aren't part of the DGA, for example Irvin Kershner. Kershner didn't want to do ROTJ anyway because he resented Lucas and Lucas never asked him because he resented Kirshner. Lucas was forced to use non-union directors because he chose to not comply with union rules by including head credits, which really is not an unreasonable demand from the union. Of course, they socked it to him with a ridiculous fine (i guess because they felt that Lucas had made so much money without proper credit sequence to the cast and crew who made it all possible--again, probably bad for the film but really not too unreasonable a dispute from the union's perspective, whose job is to protect its workers with things like proper credit).

Lucas planned on only directing TPM but then he just enjoyed working on it. He decided to direct the other two even before TPM was released, so its not an ego thing--he kept talking about how he wanted to return to directing and then he finally did because he realised how much fun it was now that he had no financial or technological pressure on him.