I have no objection to this finding. But I do quibble with Kingman's comments that it's hard for readers to broadcast their series loyalty, especially when there is no movie. As I listened to Kingman wonder about groups of dedicated book fans, I wanted to point out the pre-movie Twi-hards or the people who treat Catcher in the Rye as their very own anti-establishment bible.
The Internet, especially sites like tumblr or author pages on Facebook, have made it easier for booknerds and bookworms to find their respective fandoms. Young adult authors like John Green have a huge following online. Fans of the series remix quotes from the series in fan art. They find and comment on each other's posts. After that, I've noticed, they start requesting recommendations. Book fandoms start to resemble infinite, interlocking Venn diagrams after a while.
I think you see less real world (off line) booknerdery because reading remains such a solitary activity. We only find other fans of the book after we read it and loved it. The initial relationship is between the author and the reader. When I encounter fans of books I love, it's more like we recognize the shibboleths and move on. Even for the people who tattoo passages of books onto themselves, I seriously doubt they're looking to signal their literary allegiances.
Any road, if a reader is looking to connect with the rest of the fandom, they have only to look online.