The thing is, 4 man instances are fine and all, but what happens when there are only a couple players on in your FC and you despise the DF because of random BS?
Usually this is late night, or early afternoon. You can do solo stuff sure but why do that when you and a buddy could have some real fun running a duo.
I know in the grand scheme, that duos would be a small part of this game, still I believe that its a small part that would see a lot of use.
You cannot say that at this time SE has accommodated all group sizes. It is obvious lack of 2 player content should be a considered a "minor issue to be addressed" but an issue it most certainly is, to me and a few folks I know.
We can make this game so much more than what it is, I just want to see all players taken care of content wise, whether you are alone or only have a single friend. Although, IMO SE has done more than enough to cater to solo players.