As Tim said, the ratings changes were due to the 2000 park effects being applied to the players. Most players did not see a significant change, since most park effects do not have a drastic movement one way or the other.

The 2 ball parks (and their players) that had the most obvious effects were Houston and Detroit.

Before the update a couple of weeks ago, what you were seeing was ratings based on neutral park effects. Pitchers in Houston saw a nice boost to their grade and clutch ratings, while pitchers in Detroit saw a significant decline.

Jon