Darth Waller
Are you on the square?
I think it also has to do with his status in the Empire's hierarchy. In ANH, he was outside of the command system, the Emperor's private goon. By ESB, he had real authority and served as the Emperor's representative as well as a symbol of the splendor and might of the Empire itself. I think that kind of status requires some armor-all.
I never thought of it like that, but it sounds plausible to me.