Wizards often have to live in two worlds; that of the Arcane and the Mundane. Because of this Mundane nobility isn't as influential as Arcane nobility.
Nobility within the wizards of Tor Gizad is not based on heredity or military power or lands but rather on arcane talent. Though mundane political and military connections can influence an Arcane title to a degree, nobility commonly a reflection of how much arcane magic that the wizard can control.
The nobility of Tor Gizad spread far beyond the 'Central Tower'. In many cases the nobility will hold 'court' to serve the needs of those Arcanists within their region.