A culture which the Kal’dorei Resistance were against of, and made their own rules after the War of the Ancients.
However, the Shal’dorei, still obey and follow the rules of the Kaldorei Empire, which means, division of the people by their nobility, even though the Shal’dorei are “different” race now, the Shal’dorei are the last of the carriers of the Quel’dorei culture of the Kal’odorei Empire.
Remember the words of Elisande in the gates of Nighthold?
Elisande says: Each of you has debased your proud lineage. Each of you has forgotten the ancient power that is our birthright.
Implying to the fact that the Shal’dorei stayed true to their nature, may it not be physically, but the loyality to the rules of the EMPIRE.
Moreover,
Lady Vashj says in Serpentshrine Cavern: We are the Highborne, and the time has come at last for us to retake our rightful place in the world!
By your logic, Naga have no right to call themselves a Highborne too, as they are no longer Night elves.