If you read up on DPReview, check the A700 review for "DRO". You'll realize it essentially tries to boost the shadows (it's far more complex than that, but that's it in a nutshell). By boosting the shadows, it introduces noise.
On Sony bodies, when you're using DRO, the normal tip is to expose for the shadows rather than the highlights. This way, the darker areas are correctly exposed, but the sky (or whatever) will then get pushed down, which is far less damaging than pushing exposure upwards. This same technique should, in theory, work on the other camera brands too.
