I've seen people amend reviews in the App Stores without being prompted, it certainly helps and they tend to mention that they are updating a previous review.
As for contacting people, Apple don't make this easy. The only way i've done it in the past is to match up user names, if you can't do that then you have no way to respond to the review in any way. Hopefully Apple will change that in the future or at least allow developers to push the user towards support via email or similar.
That would be the ideal addition to iOS 7. The URL based one I mentioned would go someway to give you this functionality although it requires the app getting the data to implement the functionality. Fingers crossed are crossed for Apple to announce something to improve this in June.
"The Voyager team is aware of reports today that NASA's Voyager 1 has left the solar system," said Edward Stone, Voyager project scientist based at the California Institute of Technology, Pasadena, Calif.