FTA: "As we explored different approaches for opting-out access points from the Google Location Server, we found that a method based on wireless network names provides the right balance of simplicity as well as protection against abuse. Specifically, this approach helps protect against others opting out your access point without your permission."
Obviously, allowing anyone to enter any MAC address into a web field doesn't work. You'd have to validate ownership of the MAC address. How would Google do that?