You can tell Cailan off.. and Duncan barely cares. And he only admonishes you when he explains that Cailan is one of only a few people trying to help. So he gives an actual reason to defer to Cailan, instead of some stupid **** about kings and divine right.
This is why Loghain should've just won. 
Heh, Cailan and Anora are vastly different rulers when it comes to ettiquette. That meeting with Cailan is the Dalish elf's first encounter with the human infrastructure, which apparently isn't lost on the former, and he's too intriqued by meeting one of the famed wild elves to take offense. Remember Duncan scolding Alistair for "sassing mages"? If you had actually managed to make the King angry he would have been furious.
I have never understood if Teyrn and Arle owe fealty to the crown.
In Ferelden everyone is a ruler of their own lands.
The Banns owe fealty to their Arls, the Arls owe fealty to their Teyrns if they have one, and everyone owes fealty to the Crown. In peacetime this would mean taxes and being subject to the King's overruling and potential levies while having some autonomy in their own regions. In wartime each lord would owe the Crown a number of able-bodied soldiers taken from local militias plus horses and supplies depending on the size and population of their demesne in addition to any standing armies the lords may possess.
Apparently an Arl and above can call a Landsmeet, compelling every ruling lord in the country to Denerim to discuss national emergencies. Presumably there is a regular schedule of Landsmeets every year or two besides that. While the monarch has authority over individual lords, s/he is at least partially subject to the Landmeet as a whole on subjects discussed at the meeting. It appears that every Arling has one vote which either counts as just one or is also weighted proportionally to their size and population.
In the game's featured Landsmeets, Loghain would be confident in being able to control the ruling with Anora's vote as Queen, Howe's votes as Arl of Denerim, Arl of Ameranthine and Teyrn of Highever, and his own vote as Teyrn of Gwaren, which I think is what we see in the early cutscene that has Teagan chewing Loghain out in Denerim and being brushed off. Given the importance of Anora's support for the Warden, it's possible that the Crown's vote counts for more than any of the others. Anora's authority as Queen Dowager and Loghain's as her father and Regent are already in question by law, so it's unclear if the Landsmeet has the right to outright dethrone the King under normal circumstances.