I don't think you understand what the result means. The results apply not just to DC, but comics across the board. The majority of these "new" readers for both DC and Marvel are returning fans who have returned to reading comics via events like New 52 or AvsX. It really shows that new readership declined significantly sometime in the late 90s and early 00s.
The online surveys probably fail to capture the online fandom due to how fractured it is and how many of these fans don't even buy comics or speak English.