I think io9 is a little quick to dismiss the similarities between the Harry Potter books and some earlier works in this analysis. But I don’t think that makes J. K. Rowling some sort of plagiarist, either. Rather, it’s a matter of a monkeys and typewriters.
There are a lot of people out there writing a lot of fiction. And in the age of the internet, there are even more people disseminating it. Within the context of extent technology, class systems, gender roles, institutions, etc., those writers are going to come up with most of the possible ideas for things that can happen, staircases that people can live under, dynamics that can develop between small groups of people. And those extant technologies, class dynamics, gender roles, institutions, etc. help shape, direct, and constrain our fantasies and our sense of what will be plausible in fantastical and speculative fiction.
The real possibility for originality lies not in a single, novel concept, then, but in the juxtaposition of contexts. It’s not that a smart girl, or an orphan boy, or a magical school, or a poor but kind family, are novel creations. It’s the combination of them with centaurs, souls, vaults, prophecies, snakes, and London that matters. That alchemy is less hard to achieve than a truly new concept, but it’s still hard. It’s just too bad that more people and entertainment companies don’t even aim for that.