Ah... now we get to the heart of matters. Both Aquaman: Sword of Atlantis #40 and Aquaman: Sword of Atlantis #41 had variant covers to boost sales, as well as the new direction of the story. Aquaman: Sword of Atlantis #42 could be expected to plummet quite a bit. And while it did fall, it didn't fall nearly as far as I would have expected.
Check out the sales charts at Newsarama
, Comic Book Resources
, and Comics Continuum
for the rankings, and check them against past Aquaman sales