Both blood vampires and psychic vampires are real vampires. The main difference is that psychic vampires can feed from psychic energy (prana, chi, psychic energy, or whatever you want to call it): the life-force that surrounds and is contained in all living things, including blood, which is why the psychic vampires can and do consume blood at times. But they don't have to rely on consuming blood in order to feed and get the energy. Blood vampires, or sanguinarians, do have to rely on feeding from blood, and cannot feed psychically from other people and things. Why?

It's obviously something in the blood... But blood passes through someone's system largely undigested and unused as a nutritional item. It contains mostly water, and it also carries oxygen and other materials, which, if nutritionally required, could be taken into someone's body in more usual ways than by drinking blood. Even if blood vampires are somehow genetically changed, and have ... more specialized physical requirements, there still would be alternate ... menus available for obtaining that which we need, present in the blood.

What I am thinking, -- and this idea will no doubt irritate and annoy some people as being utterly preposterous, but please at least consider what I have to say, -- is that perhaps the blood vampires are, indeed, after the same thing as the psychic vampires. The blood vampires and the psychic vampires are all pretty much the same thing, having many simialr and overlapping traits and symptoms, but the blood vampires are unable to psychically feed from the energy, and as such, are limited to drinking blood -- to get the psychic energy that is contained within the blood!

Since consuming the blood is the only way that those who are blood vamps can feed, and they display no other psychic capabilities (and if they do, then these abilities are very limited in scope) they (quite logically) assume that it is the blood itself that the blood vamps are after. It may be the blood, or something physical in the blood, that we need, but if it is the pranic energy within the blood that we are after, whether we realize it or not, this would explain a lot of things and similarities between blood vampires and psychic vampires: the similar conditions and symptoms, the sensitivities, the feelings and sensations that both blood vamps and psyvamps experience when we / they feel the need to feed, while feeding, and after having fed.

The only difference between blood vamps and psi-vamps is that the blood vamps are limited to feeding from the blood in order to absorb the energy that they are requiring. We're all the same thing; we're all real vampires. And real vampires iz real vampires, and that's it.