While watching the opening scene from Jedi, I caught for the first time (never crossed my mind) that the Vader's shuttle comes from a regular Star Destroyer and not Executor. I wonder why that is?
I would think about it more from a cinematic standpoint: what's the opening shot of A New Hope
? The Star Destroyer! That opening shot of ANH that follows the crawl is the Tantive IV and that massive form of the Star Destroyer's hull as it flies over the camera. That shot blew the minds of many a movie-goer.
George Lucas is very much about these recurring themes in his films. And I suspect that the opening to Return of the Jedi
with the tilt down to the Death Star II and Endor, followed by the Star Destroyer passing overhead is that recurring theme returning, effectively bookending ANH and ROTJ.
I suspect that the Imperial Star Destroyer was used specifically for that cinematic device, and not for any particular plot point. And to that end, it may have also been an instance where the Star Destroyer model was much more appropriate for that shot than the model for the Executor.