We also have no idea what Sony classifies as "Top 10 Retailers" in which they sampled.... this could be just about anything from new retailers that had very few PS3's last year that now had over-stock... or it might not be.
Could be just the highest sellers (for whatever reason) including online mega-sellers that may have not been selling well for months previously anyway.
"Top 10" should be the main grounds for questionable numbers.
They may be right, still.
Numbers: Checker Players > Halo Players
Checkers Age and replayability > Halo Age and replayability
Therefore, Checkers > Halo
So, Checkers is a better game than Halo.