They may not need to shave, eat, or indeed poop (I visited this subject myself in a thread some time back), or make with the wee-wee either. Bathing is necessary though, since the dust and dirt etc of this filthy, filthy world accumulate on vampires too. They may need to take in moisture. That may evaporate away or something. Wait, they drink blood. I forgot. Duh squared. Alcohol might affect them. But then piddling would be a necessity. Well, I don't suppose the plumbing stops working... or does it? What exactly happens to all those internal organs that don't need to function any longer?
Some upkeep is required, it's safe to say, I think. And who better to handle all that, than your personal cadre of slave-women (or men, depending...). What moron of a vampire isn't going to take advantage of that? Dirk. He's just stupid enough to never think of it. Anemia, small price to pay for soaping up Megan Todd.... what are slaves for?