I'm afraid that is not entirely correct.
A Head of State, whether an Imperial, Royal or Serene Highness automatically outranks all other non-Monarchs. Prince Albert thus holds precedence over Prince Charles, even if he is only a Serene Highness, whereas Charles is a Royal Highness. Similarly, Crown Princess Masako (an Imperial Highness) is ranked equal to Camilla, even though the latter is a Royal Highness.
Royal Highnesses do very much curtsey to each other, depending on their position and rank. Kate always curtsies to Camilla, Princess Claire of Belgium - to Crown Princess Maxima of the Netherlands; it all depends on appropriate protocol and etiquette rules.
Crown Princess Mette-Marit and Princess Victoria are not of equal rank; Mette-Marit's rank is equal to Prince Daniel, whereas Victoria's - to Crown Prince Haakon. Woman to woman, Victoria does outrank Mette-Marit.
On the other hand, when Mette-Marit curtsied to Camilla, she really didn't have to because as consorts of their respective country's crown princes, they are of equal rank.
Back then, a woman would curtsey to all men upon introduction and/or bidding goodbye. Similarly, men would bow to all women. Obviously, I mean men and women of the same rank. A noble or gentry would not bow or curtsey to "lower" classes, unless he/she was exceptionally polite, or, alternatively, wanted to insult (a cold bow/curtsey was as good as a slap back then).
Love Pride and Prejudice as well, at least the original one (with Colin Firth and Jennifer Ehle).