I think the comment I read or heard related to the possible health concerns regarding the rubber crumb (I think its been banned in some european countries in various sports).
I wonder if anyone has done a long term analysis of injuries across the 3 different playing surfaces. The problem is, many factors go into causing an injury so its going to be very hard to quantify results.
Most players, when asked, seem not to enjoy the experience of playin on the fully plastic pitches.