That assumes that people in football aren't effected by what pre conceived ideas anymore than you or I, which they most definitely are. Also, it assumes that a manager is just looking for a wide player who creates chances. There are other areas to a wide players game.
I wouldn't doubt the validity of the stat, as if you look at clear cut chance conversion rates they are extremely high and much higher than general conversion rates. So that alone tells you they are talking about chances that give the striker a very favourable opportunity and not leaving him with work to do.
If you look at the chances he creates in this game you'll see how clear they are.
http://www.youtube.com/watch?v=DxVWSM1G8wg
The fact in most games he needs 4 or 5 attempts to lay on a good chance clearly effect how people even at the top of the game view him. As I said before it's just psychology. If you see a winger play 4 poor final balls, that will have a majorly negative effect on how you view him, even if he managers to lay on 1 great ball. This is a human failing more than anything. No one will think how does creating this one great chance compare with others, they'll more than likely just think about how wasteful he was, even ignoring that Lennon is one of the best, or probably the best, as getting into those opportunities where he can just lay it off far an easy goal scoring chance.