I think there is more to the iconic look than meets the eye.
One can argue that a human only PC was required for the story. That looks like a valid reason, but if you think about the other "streamlining" which surrounds it then it looks more like a requirement to either reduce cost or development time.
A human only PC reduces cost or development time for the following reasons. There is no need need to have origins (and everything that is required to implement those), the story and dialogue can be centered around a male or female human only PC, there is no need to implement (manual or automatic) race specific camera corrections in cinematics for the non-human races, and the armor found in loot only has to fit the male and female human only PC when we introduce companion armor.
When we look at Morrigan in DA:O then she has both the ability to wear a DA2-style unique "companion armor" (which gave her an unique look) and the ability to wear armor found in loot (as long as it fitted her class). That is the ideal situation for me. The player still has the option to dress her in whatever fits her class or just use her companion armor.
In DA2 BW has chosen companion armor and remove the companion's ability to wear armor found in loot. They could have chosen to do it like it was implemented for Morrigan, but BW has chosen not to do so. That has of course cost or development time reduction advantages.
The usual DA:O armor found in loot has to fit both male and female humans, dwarfs and elves and male qunari. That means each armor has to fit 7 variations. To reduce that number in DA2 the human only PC also makes sense. Now armor found in loot just has to fit the male and female humans. The companions now need their own unique armor. Let's find a great marketing term for that cost reduction operation to sell it to the players: Iconic look of the companions.
I think that answers the question raised in the topic title.