The problem is footing. The WR are a bit slower on this field which leads to overthrows (on long routes) and missed targets on the timing routes. Most passing offenses are going to prefer a fast turf. Just think about the high flying Rams (Kurt Warner era) or Mannings Colts - these teams usually struggled playing on grass. Well, I'm telling you the surface in Heinz Field is one of the worst. All that being said, I was at the Pitt game yesterday and the ground looked decent, but it is hard to tell unless you are actually down there b/c they try to disguise it. Also, ND and Pitt didn't have much trouble scoring so who knows...