"A noble's entire salary" doesn't really mean much. A ruling noble is basically running a business, with the business being his/her fief and all the methods to make money out of it. There are also landless nobles relying on a stipend from the government or other significant source, in exchange for doing work, possibly as nobles of the robe if the job was important. Some minor nobles were so poor they might not have been able to afford any servants. This was especially the case when the merchant class got more and more prosperous and powerful. This also resulted in merchants exploiting destitute nobles by being able to marry into the old nobility, by taking care of the debts the noble family had accumulated.
Of course this series is a work of fiction, so perhaps every single noble makes big money.