In other words, Gallup is admitting the following:
1. At the time it released the September 8th poll (showing McCain up by 10), it believed institutionally that likely voter results were less accurate than registered voter results.
2. Likely voter results have only occasionally diverged from the registered voter results.
3. Despite these facts, Gallup deliberately chose to release, to the widest fanfare possible, a poll using an admittedly less accurate method (the likely voter method) at the time of McCain's maximum convention bounce, knowing that it would show a large divergence (+10 for McCain vs. only +4 with registered voters) based on the likely voter method, even though such a divergence is not often present.
4. In short, they combined all possible factors in McCain's favor to make his lead seem as big as possible -- and the media went wild with it.