But completely unrelated ideas don't spawn the kind of creativity that is really useful. The point is that you want a lot of conversation on a particular topic, and some "accidents" to occur within those conversations. If the topic is "doing stuff with computers," then you'll have more computer-related creativity coming out of a place that has a lot of computer ideas bumping into one another.

This article falls into the "why are hubs hubs?" category.

Not to nitpick, but how could there be "unusually large numbers" of anything "all over the world"? What's so unusual about that large number, if it's everywhere?