There's more information about this in earlier blog post, e.g.: http://blog.pinboard.in/2011/08/a_short_rant_about_hosting/
Presumably he has gone this route in order to keep a large database mostly in-memory, but I'd be interested in hearing more about the application constraints that led to this architecture. Some applications certainly need beefy servers, but they have to provide a lot of bang for your buck to compete with the 10-50 VPSs you could rent for the same cost.