I agree that it might have been nice for some of those things. But I think putting to much effort into the interactions due to events of a game that potentially a lot of players didn't see would be assuming to much. In other words, anyone that didn't play DA2 wouldn't have been able to get as much out of those interactions, and that would have left new players confused. The focus needed to stay on this game, not the past ones.
I don't think that's a good defensive argument. Dragon Age is a game that lives its optional scenes. After all, you can actually play though the game without ever talking to any of the companions at all, that makes all companion interaction, the main component of Bioware, optional - scenes some people will never see.
Leliana, Morrigan and Alistair/Loghain interacting should be a treat for the players that happened to have that happen and not just go unmentioned at all. Even a very short or small scene would have been enough to satisfy most fans.
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- Alistair enters skyhold with Inquisitor and Hawke.
- Sees Leliana on the steps
- "Oh hey Leli, lolz"
- Sees Morrigan in the doorway to the castle.
- "Morrigan?"
- Morrigan turns around and walks away.
- "Good to see you too..."
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There, 20 seconds. 