That's exactly it. The Core books are primarily about getting the rules out. There are other books that will contain the "fluff" rules.Roleplay is something the players and GM have to add... it's not something that can be mandated into the rules.... and least not without coming off as artificial.
Truth be told, I can see Ravenloft coming out in 4 main books:
A Player's Guide that talks about the relations between players and the land, like a few classes, maybe a race or two. New feats and items would be in there too.
A campaign guide, which gives you information about the Domains, akin to the FR Campaign guide.
A Dungeon Master's Guide, with rules for power's checks, curses, madness, customized monster templates for older or more unique monsters. Perhaps even guidelines for customizing those templates.
And finally a Monster Manual, for the special monsters that Ravenloft has always had to offer...