Hacker News Reader

How do they collect this data? Do they have chrome store crawlers?

Yeah they must. I wrote one once too to power this: https://extstats.appspot.com

I wrote it to track our competitors (I used to work at HubSpot) but you can add any other extension in the drop down on the left.

What happened to it?

Also, how do you deal with duplicately named extensions?

Yes