Rear bearings out at 19K on 03 OBW

Found out this week that the source of the grinding noise came from the rear bearings. Dealer replaced both of them under warranty. I am told that water had gotten into the bearings and there was a lot of rust around the area. I am puzzled by water getting into the bearings and since there is only 19K on the car, it seems a little premature for the bearings to fail. I am not sure if anyone else has experienced this problem. My last subie had 150K on the orignal set of bearings.

I am wondering if I should have the fronts checked out too and how would I go about getting the dealer to do it if there is no noise?

danz