His productivity didn't drop as much as his usage.
If healthy, I think he'll end up with 750-850 yds, and 6 or 7 TD's over the remaining 13 games.
2009 - 16 games - 1108 yds, 7 TD, 4.6 ypc
2010 - 16 games - 1273 yds, 13 TD, 3.9 ypc
2011 - 15 games - 928 yds, 9 TD, 4.1 ypc