The scripting says otherwise, and I just ran through the boon ceremony with both an Amell and a Mahariel, and he's no-where to be found. So... screencap?
As near as I can tell, the script you posted appears to set the character that will stand with your Warden and then be available for a chat. In addition to that character, the scene includes several human noble attendees sprinkled in amongst the crowd - presumably by royal invitation. Would those invitations not include the highest-ranking non-royal noble in the land? At least one of the nobles standing there very much resembles Fergus - so it's not unreasonable to interpret that scene as including him.
Ohhhhh. Interesting theory. Headcanon accepted!

I think most people believe that Loghain & Howe conspired to kill the Couslands and Cailan to take over Ferelden. It's certainly a rational, logical conclusion - but it's not the only one.
If Howe was the opportunist I suggested, it implies that Loghain may not have known of his plans beforehand, and that Loghain might have actually left Cailan swinging at Ostagar due to battle conditions at the time, rather than as some pre-planned plot to kill him. Of course, a lot of people also believe that Loghain tried to kill Arl Eamon with the poison, but Gaider claims his intent was only to keep him out of commission for a time - and the elf stationed at Redcliffe's Tavern was there to monitor the situation, so that an antidote could be provided if Eamon took a turn for the worse.
I'm actually kind of glad that there were some blanks left for us to fill in. Not only does it make for a lot of interesting forum discussion, but also expands our opportunities for role-play.
Yes pretty much that, it is because Cousland Terynir is next to the kingship, while the writing goes on and on about Alistair being the heir of the throne, it don't do much justice to HN who is the last known living heir to Cousland Teyrnir. Among the companions only Wynne address that. Noble NPCs only say "you look familiar....", only Jory feel honored meeting "Lady Cousland".
Well - I suppose they could have done a bit more with that than they actually did. Given the number of unique origins they were trying to support, there's only so much unique content you can reasonably give each of them. Also, you have to consider that the vast majority of regular citizens you encounter would probably have no idea what any of Ferelden's nobility looks like, never having seen them. It's not like they could google them - they don't even have photography in that setting.
Also, I think the writers wanted to present Fergus as a surprise at the end, so they trod lightly around anything having to do with the Highever Terynship.