What you're talking about (massive ground-level driving effort to pinpoint where along streets specific addresses are located) would boost accuracy. Without a Google level address parser, though, you don't get usability for a lot of use cases, which is frankly much more important for a lot of companies. One of the best things about Google's geocoder is that you can throw various location names, as humans type them, and Google will return something, and it's usually the right thing. For many applications, this is the desired behavior, rather than precision.