Different magics have different bases.  As such, some
worlds are biased towards specific types of magic.
The more obvious examples are here:

Healing:
  The prolific life on Sosel and Wysoom lend extra vigor
to healing magic.  The lifelessness of Crypt and Raji
impede healing magic.
  Healing from the Powers of:
    Good: Impeded on Crypt, aided on Welstar
    Evil: Impeded on Welstar, aided on Crypt
    Neutral: Impeded on Welstar and Crypt, aided
        on Sosel.

Abjuration:
  The simplicity of Crypt and Raji aid abjuration spells.
The prolific life of Sosel and Wysoom impede abjuration.

Combat Magic:
World     | Enhances           | Impedes
__________|____________________|____________________
Crypt     | Cold, Disint.      | Illu., Elec.
Perdow    | Harm, Unholy       | Acid, Holy
Raji      | Elec., Illu.       | Asphyx., Disint.
Sosel     | Fire, Poison       | Cold, Harm
Welstar   | Holy               | Poison, Unholy
Wysoom    | Acid, Asphyx.      | Fire