That's true, if the Emperor's arrival started it, maybe. It's been a little while since I watched, is there an extra overhead Star Destroyer shot--if not in that scene, in another?

Also, now that we're talking about briefing scenes, is there any chance of replacing the DS graphic in the ANH briefing? I'm half cringing as I type this just from being used to it (and they are kinda cool in an old school way), but given the quality of the graphics in AOTC and ROTJ, the only explanation I can see for them looking like that is the status of the Rebellion at that point. They were just winning their first big battle, so that could definitely go for the explanation, but if you don't want to go with that and if it's feasible, it might be something worth looking into.