Whilst previously Google let you review and rate local businesses for all to see they now let you add and edit map placemarks. In US, Australia and New Zealand at least (why just those?).
It’s a smart move to encourage users to correct and enrich their geo-content. Depending on your philosophy, you may prefer to contribute to OpenStreetmap but satellite images don’t come cheap and there’s no question that Google can do it bigger and slicker.
The general perception is that Google Maps is a public web utility anyway so why not contribute (except you live outside the US and Australasia)?