Perhaps it's just my biased reading sample, but it does seem to be stronger than the fairy tales themselves would warrant. Sure, they exist in plenty. Indeed, you have the king being pleased in Iron Hans that the heroic young knight is a prince, and the princess maintaining that she knew he was no mere gardener's boy when she first saw his hair. You have The King Who Would Be Stronger Than Fate and all his fellows trying to avert a mesalliance, with noticable lack of success. But Rapunzel marries the prince despite a noticable lack of birth (inverted for Disney, but still there). In Catherine and Her Fate she ends up queen despite being a merchant's daughter who lost her fortune. There are kings, like the one in The Seven Foals, who faithfully carry out their promises about who shall marry their daughters, and even princesses like the one in The Fire-Bird, the Horse of Power, and the Princess Vasilissa who decide the man who brought them to the king is better than the king. Or you can end up married to the ogre's, the witch's, even the Devil's child, as in Prunella.
If they were aiming for realism, that would be another thing. Some kings and queens chose to marry off their children like sound, prosperous freeholding farmers, down to and including wanting their daughters-in-law to be good housewives and hard workers. A more realistic setting might touch on political implications. But these happen even in worlds where everyone knows all the tropes, where a princess is in despair because the evil fairy came to her christening but was appeased and went away happy, without cursing her.