Farther West Than West
Magic is not uncommon throughout the world, but powerful magic is. Nearly every village has a local wizard capable of simple spells of mending, healing, etc. These wizards are usually taught by the preceding local wizard, which more often than not, is also a member of the family (parent, uncle, etc.) Truly powerful wizards are almost always graduates of the School of Wizardry on Roke Island. The school is governed by the Archmage, and the school operates independently of any the Houses.
Regarding divine powers, similar rules apply. Many are gifted in the divine arts, but few are truly masters. The temples train individuals as they see fit, and again, family ties play a heavy role. The temples are not wholly independent; their ability to operate is subject to the whims of the House on whose land they use.
Primal power users are rarely seen in the Great Houses; they tend to be found in the Lesser Houses, particularly the more tribal/nomadic.
Psionic powers will not be allowed in this game.