Ul'dah's nobility is tied to money. I think this is stated, and I'm quite sure it was mentioned before on this thread. If you are rich, you are a noble. Ishgard seems to follow a more traditional type of nobility. An Ishgardian noble can still be a noble even if he has no money; an Ul'dahn's nobility is directly tied to his pile of riches.
The only city state without nobility seems to be Limsa Lominsa. Gridania does have nobility (as per the Haukke Manor quest), but the way in which one becomes a noble is not clear at all. Maybe the owner of the manor was the remnant of some old political system? Because I don't think you see any nobles mentioned in Gridania proper. Or maybe they were foreign nobles that somehow got ownership on the land. I forgot if the storyline ever mentioned how that lady got to become a noble in the first place.
The only city state without nobility seems to be Limsa Lominsa. Gridania does have nobility (as per the Haukke Manor quest), but the way in which one becomes a noble is not clear at all. Maybe the owner of the manor was the remnant of some old political system? Because I don't think you see any nobles mentioned in Gridania proper. Or maybe they were foreign nobles that somehow got ownership on the land. I forgot if the storyline ever mentioned how that lady got to become a noble in the first place.