And minutiae about court cases, legal precedent of the era.

Similar with Count of Monte Cristo as well, the details of the Mediterranean smuggling trade it goes into is simply amazing.

I don't know about the other books off the top of my head, but Count of Monte Cristo and Dumas' other works were published as serials in a newspaper, where I'm pretty sure he was paid per word. Such a system really encourages going into detail with things that are not exactly relevant to the plot :)

(I love all of Dumas' works)

20000 Leagues Under the Sea also came to mind.

Perhaps, but I do remember it being smaller than Les Miserables, Monte Cristo etc which are massive, almost 1500+ pages of material in each of them.

Ha, so many pages of exhaustively cataloguing aquatic species.