I certainly remember the scene you're talking about, I don't remember that explanation though. No biggie, I'm sure you're right, for that matter I'm rereading the series right now (off and on at least). I'm at around chp 50 so I'm sure I'll come across it again sooner or later.The issue with the shrine maidens parents was covered fairly well in the earlier-ish chapters, as was noted by Shizuku. When Nagi and she went to the main island, they noted her mother was among them that were giving reverence. Because the maidens are revered as Gods, they are segregated as they are no longer 'people.' The exception would be Karin, in which case it hasn't been said where her parents are located, or if they're even alive.
As for 'other parents' in the series, I haven't been bothered by it. The focus of this work is the Dragon God, his interactions with the Cape Maidens, and the island, using other characters as temporary mediums (mostly Tamae.) Because of this, you see very little interaction with normal people whom may have parents at home. It could also be said that the older generation gets help on manual labor from their grandchildren, while the parents work in businesses on the main island.
So, segregated out of society as "non people"....doesn't sound like too happy of an ending to me. I mean as I remember the scene her mom was ignored. I guess that's part of what makes me wonder just how "happy" an ending we're heading for. Of course there's really nothing right now but guess work, since the Dragon god was reincarnated after hundreds of years we've really got no precedent to look at as to how things will play out.