I might've answered my own question, after bouncing various ideas off people. >_>
And they both revolve the same thing; the "magical lifeforce shell" that surrounds a living being. It's basically a randomly and uniquely created flow of magic inside the body, powered by the soul. This basically creates a sacred "area" where foreign magic cannot enter. This stops the idea of, say, a water magic user allowing himself to press all the blood in the body to a certain point, killing the person instantly. When a person dies or is killed, the soul is seperated from the body and sinks to the ethereal, AKA spiritual plane. This basically makes both the soul and the body fair play for manipulation by magic.
This is where necromancy comes in. Necromancy can mess with the body, reanimating certain parts, using their own magic as a mimic for the shell. Necromancy can also seal souls and manipulate them in many various ways.
The reason why a necromancer can't truly bring back life or create life in it's purest form; the soul can be put back into the body, but it's nearly impossible to recreate the shell. This opens the body to eventual corruption.
The reason why the use of necromancy makes, in general, the user look somewhat more sickly is that the use of it negatively effects their own shell. Use on themselves makes this more apparant, much more.
Oh, and necromancy also can be used to attempt to strike past the shell and at the soul itself, but not the actual BODY. This sort of necromancy is very high level, and requires contact, meaning you can't just stand away and drawn the pattern.