I doubt it adds a ton of new data. Or that all but the simplest roads drawn by hand by an amateur wouldn’t be reviewed and redrawn by a professional, but Google is smart to include this:
There is a class of user that would be disappointed not to be able to submit GPS-collected data. But they’re all doing that with OpenStreetMap.org anyway. One thing for sure: Apple never thought of this…and, to be fair, Bing/Nokia/Navteq hasn’t either (although their data collection via UPS and Fedex is huge…3 billion miles driven annually).