] It is merely a supposition, but perhaps JA uses the word 'obey' to highlight again the almost father/daughter like relationship that exists between Darcy and Georgiana.

I agree. People used to have a much more positive attitude toward obedience than we do now, especially about chidren obeying their parents. Some of the most popular Victorian children's literature (post-JA, I know) is full of heavy-handed reminders that good children should always obey their parents, and of the terrible things that happen when they don't. I think JA was definitely trying to show that Darcy and Georgiana have a good, loving, but unequal relationship, as between parent and child. Apart from their age difference, Darcy has literally been a father figure to Georgiana since she was ten(?). I'm not sure if Darcy realizes quite how unequal their relationship is. (There's more evidence for this at the end of the book, but I won't go there now! ;-)