I think there's a bit of a myth surrounding Arteta's style of play, probably because of his time as a attacking midfielder/wide player a few years ago. Despite being considered the 'attacking midfielder', he's more often than not online with the defensive midfielder, and takes up as many defensive duties as they do.
http://vimeo.com/16362156
That, for me, is a typical Arteta performance. Look at the amount of times he picks up the ball in deeper positions, and is behind Heitinga, rather than infront of him. Positionally, his style doesn't change much whether he's playing alongside Heitinga, Neville or Fellaini. He has to take the ball more alongside Heitinga because Johnny, for all his qualities, doesn't always get involved when we have the ball. I think that comes to how much space he has, rather than shying away from the ball. He's a centre back really, more than anything, and whilst he is an excellent passer, he doesn't have the touch, close control and agility of a typical midfielder.
If he played like he did against Stoke every week I'd agree with you, but he doesn't, and Fellaini offers alot more consistency in this area. I don't think the big man is outstanding in possession, his distribution is simple stuff really, but he takes the ball much more than Heitinga. Defensively, I don't think either of them are outstanding, positionally, they are both behind Neville and even Arteta. They both have a tendency to leave big gaps in midfield.