Нашёл в оригинале; да, это не косяк перевода, так и есть. Чёрт, численность волшебников - 20к, не больше, скорее 12-15к. Общемировая не более миллиона, скорее полмиллиона. Не самый крупный областной центр. Все друг друга знают в мире, причём реально все и всех.

Видимо, 100к на квиддичном стадионе - это включая гоблинов и прочих русалидовейл, иначе сложно представить такую концентрацию волшебников.

Добавлено 01.07.2015 - 07:39:
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Цитата из роулинговского интервью:

JKR: Well, Hogwarts. All right. Here is the thing with Hogwarts. Way before I finished “Philosopher's Stone,” when I was just amassing stuff for seven years, between having the idea and publishing the book, I sat down and I created 40 kids who enter Harry's year. I'm delighted I did it, [because] it was so useful. I got 40 pretty fleshed out characters. I never have to stop and invent someone. I know who’s in the year, I know who's in which house, I know what their parentage is, and I have a few personal details on all of them. So there were 40. I never consciously thought, “That's it, that' s all the people in his year,” but that's kind of how it's worked out. Then I've been asked a few times how many people and because numbers are not my strong point, one part of my brain knew 40, and another part of my brain said, “Oh, about 600 sounds right.” Then people started working it out and saying, "Where are the other kids sleeping?" [Laughter.] We have a little bit of a dilemma there. I mean, obviously magic is very rare. I wouldn't want to say a precise ratio. But if you assume that all of the wizarding children are being sent to Hogwarts, then that's very few wizard-to-Muggle population, isn’t it? There will be the odd kid whose parents don't want them to go to Hogwarts, but 600 out of the whole of Britain is tiny.

Let's say three thousand [in Britain], actually, thinking about it, and then think of all the magical creatures, some of which appear human. So then you've got things like hags, trolls, ogres and so on, so that's really bumping up your numbers. And then you've got the world of sad people like Filch and Figg who are kind of part of the world but are hangers on. That's going to bump you up a bit as well, so it's a more sizable, total magical community that needs hiding, concealing, but don't hold me to these figures, because that's not how I think.

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Три тыщщи волшебников во всей магБритании. Блиииин : ( какое там всевластное Министерство, какой Вольдеморда.

Какой кошмар : (