While being noble is, in the 10th Age, far less restrictive than being a noble in the Renaissance of the 17th-18th centuries, there are still barriers towards advancement that must be hurdled: proving, for example, that you owe no servile duties. In Dorlan things get even more thorny, as only mages can hold appointed or elected positions within the Dorlish state.
So, there is a sort of bifurcated situation between the two. It would help to understand how the noble families came to power, I think. Most nobility in Dorlan has arisen through trade and mercantilism, making it unique amongst the northern kingdoms (or at least causing it to stand out) since the raising of men is of much less importance to the Dorlish state. Therefore, nobility do not eschew, frown upon, or in any way denigrate mercantile work—it is their lifeblood. Almost all noble families began as urban merchants who rose to the rank of patrician by their investments, trained a child and some other kinsfolk in magic, and inserted themselves into the world of political power.
However, there is still a need to raise troops, to have trained fighting men, and to have knights to do battle. Additionally, while the institution of the College of Silano (much more like a medieval universitas than a modern college in that there are no "classes") and the numerous private tutors that make their wage by training young folk to be wizards can produce great numbers of semi-skilled magi in comparison with other lands, there are still not enough to govern each and every plot of land in Dorlan.
Those members of the Patriciate who do not manage to gain the learning required to enter the Dorlish state may sometimes find themselves appointed to rule over the family lands (which are owned explicitly by the family, not by the government or by feudal right). These men and women become the Dorlish barons and baronesses—no other title is recognized in Dorlan for landed nobility. Over time, these second and third sons develop their own branches of the patrician family, ones which are headed by military leaders rather than mages. Still, the desire is strong for a baron or baronness to train some of their children as mages in order to ascend the ranks.
The rural barons are contrasted with the urban magistracies and councils; cities of a certain size do not belong to any individual family, but rather achieve commune status. Their citizens are free and unservile men, and they are generally governed jointly by a council of elected local patricians (who must be wizards) and a magistrate appointed by the High Mage of the province in which the city is located (who must also be a wizard). Thus, rural government is generally non-mageocratic while urban government relies heavily on magicians for functionaries and high offices.
This further enforces the Dorlish social structure relying on magic, for money is the barrier to being trained as a wizard. Thus, the families who manage to secure lucrative trades and mercantile contracts are those with access to enough resources to make their sons and daughters into wizards, which means they also control the government... and regulate in the favor of merchants. Thus Dorlan manages to reproduce its own society in ever-tightening or strengthening iterations.
The very first thing I see here is backlash. The society has few control valves for those who are ambitious but poor or ambitious but not smart enough to be wizards. While the second class is in the minority, there are still social pressures that have few ways for relief. The most telling outlet of this was the so-called Malvaran Uprising of X.389 in which several barons in Malvaro as well as many crowds of peasants, Hashtemite priests, and outlaws attacked and sacked the city of Monteno and killed its urban council and magistrate. The Malvaran League was at once declared traitorous to Dorlan and the other provinces engaged in a 3-year war to subdue it—at the end of which, the fields were destroyed, the manors of the offending lords torched, the Malvaran patriciate families which had participated were exiled, and a great famine struck the mountainous western province.
So, while warriors and knights do hold status with Dorlan, it is a far lower status than their wizard brethren... and the merchant-houses like it that way.