If you have 11 Crouchs in team, you may have to wait 264 hours (11 x 24 hours) before scoring a goal. But seriously, tall players are slower on the ground. They can take care of the high balls, but they need to be fast on the turn to deal with speedy players. I don't fancy Crouch as a central defender.
adding to what you are saying SohCK, apart from speed on the floor and turning, crouch doesn't really have a physical presence that a defender needs.
if he was stronger and used his body more, he would score far more goals than he does now. unfortunately, he is a gentle giant in every sense of the word. you can't really teach someone to be more aggressive, you either are or arn't aggressive. and crouch isn't.