Harry Potter reproduces the same structure.
The deep story is loyalty. Harry, Hermoine and Ron will risk all for their friends, especially each other. This is the same deep story as The Lord of The Rings, Star Trek, and The X Files: myth-based narrative series with passionate cult followings.
The relationship between the central characters is that of surrogate family. This is sometimes explicit in Star Trek, where during moments of self-doubt the unmarried captains mention it out loud. In LOTR and X-Files the main characters have rich family backgrounds from which they have removed themselves. The LOTR characters are on good terms with their left-behind relations, while the X-Files characters are estranged to some degree from their childhood families. In the present day Muldur's monofocus is comically monastic. Harry Potter is the only child in this group. His isolation is at one and the same time the most radical and the most traditional, relying on the fairy tale motifs of foundling child and evil step-parents so that his newfound family substitutes are a welcome refuge.
The depth of emotion with which consumers of these narratives invest these characters seems symptomatic. It's stronger than simple imaginative transference, filling a more or less consciously perceived need for family bonds, particularly loyalty.