Wow, some people really don't understand this do they?
I'll try and be blunter. We have lots of people who might be classed as a DM on Football Manager or whatever game you are playing, but the reality of the situation is that DM is a complex position that seems to be a catch all for any midfielder who can tackle.
Barry isn't a DM. He's a centre mid who has played there every now and again.
Viera is a centre mid.
Kompany is a centre back.
Toure is a box to box midfielder with an emphasis on defending.
Zab is a utility player who can fit in as an anchorman every now and again.
De Jong is an anchorman.
Milner is a box to box midfielder with an emphasis on attacking.
In reality, we have one and arguably two defensive midfielder (De Jong, Barry), and none that can actually pass the ball more than ten yards. I'd be surprised if either were these were still at the club by the start of next season, we don't play the type of football that suits either of them. Barry would probably stick around to rotate in and out of the team with the Viera type of mid.
De Jong will get many, many games this season as Mancini will play an anchorman as we lack a creative defensive mid, which is why we're far more defensive than his Inter team despite using the same setup. In January, or more likely next season, he'll pick up the player he wants and De Jong will be sold.