Of the 2000 servers, about 90% of them are running something related to WordPress.com. There are 36 "load balancer" servers in total. I added up the req/sec across those 36 machines and came up with the 70k/sec number in the article. The requests aren't evenly distributed across that subset of machines though, so you can't just divide evenly to figure out a req/sec/CPU rate. I left another comment in this thread that mentions 5k req/sec on a "normal" load balancer and that the limiting factor isn't Nginx CPU usage.