Never used a a630 but have a A85 and an S3. As you rightly picked up the major difference is the 12x optical zoom on the S3. There appear to be a few extra features on the S3 one touch movie mode, stereo microphones, Larger physical size, 6 Mp instead of 8 Mp on the A630, Faster continuous mode, 2.5 fps i believe, Image stabilization (a major factor). Image quality I can't really say as I have no experience of the A630. A few sites say that the S3 is slightly better, but often this is in the eye of the beholder but the S3 is definitely better than the A85 across the range.
I think it depends on what you are wanting your camera for, the A630 looks like a great point and shoot camera with lots of extras if you want them (like the A85) whereas theS3 is a point and shoot camera but really needs one to use its various functions including M mode to bring out the best, possibly could be described as a slightly more technical camera. Hope this helps.