Without getting too detailed...
Different pickups sound different based on a couple of factors.
1) The type of magnet used. There are ceramic and then alnico. Under the alnico, there are several different varieties.
2) The size of wire that was used. I don't recall off the top of my head their exact sizes, but there are different gauge wires that winders will use to achieve different tones.
3) How many windings there are. Typically, the less amount of windings, the less output a pup will have, the more, the higher output it is.
That's it in a nutshell... Also, those basic principles would apply to any brand of pickup rather it's OEM Jackson pups or name brand such as Seymour Ducan or Dimarzio. Then there are also boutique winders as well.
Also, something else I should mention, the proximity of the pup to strings will also have an impact.