I definitely agree that if that was the case then Bethesda is going downhill, and I am not happy about the vampires in Skyrim because there is no explanation, I was just saying it is possible that in the 200 years that have pasted in TES the Volkihar could have seen that if they want to compete with the Order and survive they need to be able to bland into society to help manipulate it just as the Order does.
It wasn't the Volkihar that made a daedric pact in order to blend in, i believe it was one of the other clans of Skyrim. In the book "Immortal Blood", it does not say the Volkihar was the only clan in Skyrim, they were just the most powerful clan in Skyrim. It's entirely possible that one of the other clans made a daedric pact, with oh say, Sanguine, and became the "Sanguinare", able to blend into society.
I think Bethesda actually originally planned to flesh out the Volkihar as a seperate strain that the player could contract and join, but they couldn't due to time restraints, so threw in what they did have "done", the "Sanguinare". Otherwise, why have vampires that are just "Vampire", and have vampires that are "Volkihar Vampire"? Not to mention, we were shown concept art of a Vampire that noone has seen in game yet, and she looked different from any Vampire we have seen before in previous TES games, almost like a "Primordial" or "Proto" Vampire. http://3.bp.blogspot.com/_4lrm97dBqNo/TUFlxQiW7CI/AAAAAAAAAZM/n_xn6TWnSA8/s1600/artofskyrim_013_femmonster.jpg?__sf=1303445029 It's likely that was actually concept art of "Lamae Beolfag/Bal" herself. Why do concept art of her, if she's not gonna be in game? They planned to add more than they could at the time. This, combined with how the Vigilants of Stendarr feel like there should be more to them and are "unfinished", leads me to believe that we'll be seeing a DLC involving Vampires sometime.