The "pro" cameras have real weather seals. The D200 as a "prosumer" crossover camera has seals but they're not as robust as the real pro cameras. I'm pretty sure the lenses also have different levels of sealing, and only the really expensive pro lines of lenses will have any real tolerance to dirt and water. Even so, you always see the pros drape plastic over the cameras so the rain isn't beating directly on the camera...