Another interesting sequelae to this kind of interest seems (well, okay-- anecdotally) to be an eventual interest in and participation in RPG gaming during preteen/teen years (and in some cases beyond).
In that case, I think that interest in this book series can serve as an early indicator that kids have that set of interests and innate needs (socially and intellectually).
ALL of my DD's RPG friends (and this is at least a couple dozen kids) were interested in these books to the point of obsession during elementary/middle school, and all of the friends that were so fixated on them back in the day (again, at least a dozen or so of them) are now playing RPG's both regularly and often mutliple platforms/characters. Both genders.
I don't know if there is a real causative connection. But there certainly seems to be a very strong correlation.
