He is happy here, don't be deceived by his attitude. He's a laid back player, we have quite a few of them at the club. Saha, Yakubu, Fellaini and Yobo all spring to mind. I don't have a problem with that.
He just doesn't have the tools, he's a poor athlete and to be honest he's not a great footballer either. He doesn't even attack the ball well enough to be dominant in the air.
Cahill and Saha are superior headers of the ball.