I think they're a little more common where I live in the UK, at least. I actually thought the original post was going to be about https://www.the-bookshop.com/ in Scotland where I've visited a few times, but they have 100,000 books versus this guy's 150k :)

I don't know if the US has the concept of "book towns" but there's quite a few over Europe where you'll have used book stores very close to each other and some sort of annual book festival. Wigtown in Scotland is absolutely tiny (under a thousand people and far from any major towns) but has several, as does Hay-on-Wye in Wales. It becomes a bit of a tourist thing.

I don't think so. As I said, Harvard Square used to have a pretty high density of book and music stores. Not really so much any longer and I've never seen the equivalent elsewhere. Of course, Manhattan has a lot but, given the population density, I'm not sure I'd call it a book town.