I think the club a player plays at, and the way that team plays affects the player's quality immensely. Look at Owen from a few years ago, and look at him now. Gerrard Houllier ruined him, he's instilled in him this idea of waiting for long balls to come to him.
If you look at the 18-20 year old Owen, he's a constant menace, always shaking up the defense, maybe dribbling through a few defenders, now look at him. I also think Man Utd spoiled Ruud a little, not in his finishing ability, but his hunger to go attack a defense on his own.
I'm sure if an attacking coach like Wenger, or Sir Alex bought Owen, he would be a world beater, so hopefully Rooney gets picked up by a bigger club and develops properly.