Riewoldt gets the best run out of all the forwards. Brown, Fevola, Mooney and Franklin get absolutely nothing compared to him. It's not his fault, it's the umpires.
They play different styles so I'm not sure you can compare them. Just because they're all playing the same position doesn't mean they're playing the same game.
Riewoldt very rarely initiates contact with his opponent in a one-on-one. Almost invariably he leads his opponent to the ball and puts his arms up to mark it. When caught underneath a high ball, if there is grappling, he's usually the first to let go and leap for the ball. Watch him play and you'll see this.
Given this style, he's far more likely to get frees. Hall, especially, has a completely contrasting style of initiating contact in every situation. Brown and Mooney do this a fair bit as well. Franklin is unpredictable but just as likely to get caught in a one-on-one with the ball coming down on his head as on a good lead. Fev tends to get the ball on a lead, but when caught in a one-on-one he's pretty poor, so he gives away frees as well.
It's about their style. Watch the game carefully and you'll see that.