Thank you both for your suggestions.
Strangely, the S3 doesn't seem to follow the rules. Yes, I could download the CRW (DNG) files through USB using Windows Explorer, but not via Canon CameraWindow, like I can with the SX130 CR2 (DNG) files. I think I've tried every possible combination of file prefix and extension, and have restarted the camera with each option change, still no go. I will continue with this and report back any positive findings. Thanks again.